Coloured Bricks, Pick-Up Sticks
by Wyrvel
Summary: Midoriya Izuku is a very warm person. Not his personality (though that's also true). It's his quirk. His quirk is that he's warm. (Quirk meta/Quirk-Obsessed Izuku AU)
1. Heat Resistance Is A Superpower

**Experiment One: Heat Resistance Is A Superpower**

* * *

Midoriya Izuku is a very warm person.

Not his personality (though that's also true). It's his quirk. His quirk is that he's warm.

Izuku has had his quirk since he was born, burning his way into the world at a hearty temperature of "barely feverish", and it's never dropped since. According to Books, which Izuku reads a lot of, this means his quirk is Morphic; he is quite literally _made_ of warm.

His dad was Morphic too; his insides could catch on fire and there was so much of it he could even breath it out. There isn't a lot of use for a quirk like that, but it looked pretty awesome. According to the doctors, Izuku has received his father's quirk. He loves it.

When Izuku is four, he gets to go to daycare, where he impresses everyone with it. Morphic and Shape quirks are impressive to small children. There's a Shape kid with a big tail, and everyone wants to be his best friend, which proves the rule.

Izuku, on the other hand, decides he wants to be Bakugou Katsuki's friend. He's loud and pushy and probably has an Energy quirk. Something like fire. When Izuku pushes to be his friend, Bakugou Katsuki says once Izuku finally figures out how to set himself on fire, Izuku can be his sidekick.

To Izuku, this is a wonderful idea, a dream come true. The first thing he had ever grown attached to was a news broadcast where a hulking blond man walked straight out of a comic book to rescue a seemingly infinite amount of people, laughing all the while. Izuku could watch that video for hours. In fact, he _does_ watch it for hours. Daily. He wants to be a hero like All Might more than anything.

Izuku thinks that it's wonderful All Might has the power to save so many people and bring hope to everybody. Katsuki thinks it's awesome that All Might strong and everyone loves him. They are four years old, and to four-year-olds, nuance is fake.

But they both watch the newscasts of this _saviour of the new age of superheroes_ , and Katsuki is a magnetic kind of person who makes friends instantaneously, and he looked at Izuku and said "you can do this with me".

The heat didn't prickle at his cheeks, and his skin didn't flush, because he doesn't know what it means to heat up, and he doesn't even know what cold _is_. But if he could, he'd have blushed with pure joy.

He wants to be a hero.

* * *

Kacchan's quirk accelerates, and his behaviour along with it.

Izuku's quirk and personality, on the other hand, are at a standstill.

He's never gotten any warmer, and he's never gotten any braver, but Kacchan's boisterous attitude has jumped from "bossy" to "outright violent".

His quirk is explosions. They scatter from his fingertips, sparking off the sweat on his hands. Reactive quirks are impressive; Izuku knows this because the teachers won't stop telling Kacchan how impressive they are, and how wonderful it is that he's gotten one.

At first, Izuku is ecstatic, and heat rolls off him like sun-warmed pavement; he's a perfect sidekick. He's practically a _recharge station_.

But, as stated before, Kacchan's behaviour accelerates.

 _A lot._

It starts with "You can read it like Deku, that means useless!", marring him with an obscure and unpleasant nickname forever.

And Izuku ends it somewhere around Kacchan shoving a kid to the ground and marching forth, hands sparking ominously.

Izuku is five and a half and he's watched at least fourteen recordings of All Might standing up to bad guys and Kacchan isn't a _bad_ guy, is he? But he still stands up, puts up his fists, and tries not to cry.

Kacchan's heat can't touch him, but he and his friends have fists, which are just as good.

* * *

Izuku spends a lot of time being angry.

Not… _angry_ , angry, like Kacchan is, but so frustrated that the warm air rises in great billowing puffs that make his blanket float off him. He simmers. Clenches his teeth. Complains a lot. He is five years old, and there's nothing five-year-olds love more than whining incessantly.

"He's not _heroic_ ," Izuku insists over dinner for the eighth time, "he beats up kids which is _villain_ stuff."

"I'll talk to his parents, sweetheart," says his mom.

Izuku doesn't think that's enough.

Well, it _technically_ is; Kacchan doesn't attack people after that. But he doesn't stop being _mean_. He still includes Izuku and seems to want him there, but Izuku spends a lot of time being angry all the same.

Most of the time, they go hang out at empty lots where Kacchan can use Izuku's warmth to gather up his sweat. He says that the more you work on it, the stronger the quirk is going to get. Izuku ("Deku") is fine the way he is, Kacchan claims, since the muggy ring of heat radiating off his skin is pretty much perfect for gathering sweat, but it'd be way cooler if he could light his skin on fire at some point.

Maybe like green fire, he continues, because the dull, dead-leaf pallour of his hair would look 'stupid and ugly' with normal fire.

Izuku scowls at the gravel, takes a drink of water and breathes out steam. That happens sometimes. His insides are hotter than his outsides, like his dad, and he…

It is at this point, Izuku, age six, suddenly realizes that he can't actually turn his quirk off.

He's gotten into heroes as an industry by now. He's been paying special attention to people with quirks that work like his do, like Endeavor, who has the same quirk as his dad, except on his outsides, and it _looks_ like it's always on.

When he gets home Izuku meticulously records notes and compares them and then starts looking up as many Morphics as possible until he stops dead at the obvious conclusion:

There is no existing hero who has a Morphic quirk that's just kind of _there_.

He doesn't know what else to do from there, so he stares at his notes for an hour until his mom calls him for lunch and then he never mentions it to another living soul.

* * *

This is the story of an eight-year-old.

Initially, I mean.

* * *

Izuku, age eight, loves experiments.

His quirk is weird and no one really _thinks_ it's weird? But the thing is, weird quirks, you can do weird things with them. Heroes are good at that. And anyway, heat is the most common kind of Quirk ever and everyone has a bajillion ways of using it so Izuku is _enterprising_ by wanting to do weird quirk stuff.

He gets an All Might lunchbox for his birthday, left to the side when he and his mom go out to celebrate, and it's not until the next morning that he actually moves to put it on the shelf with all his other All Might collectables. But his fingers trace along the indents in the metal and his brain hits the phrase 'melting point' so fast Izuku can't remember the thoughts that brought him there.

And Izuku, who loves experiments, decides he likes the thought anyway. He collects his notebook and his pencil and his eraser.

Now all he needs is a blowtorch.

He'd ask Kacchan but Kacchan will never let him test how hot his explosions get, and he'd ask someone else with a heat Quirk but everyone else's heat quirks are different and Izuku isn't supposed to talk to strangers.

He also isn't allowed to take people's blowtorches without permission, but he's, uh, borrowing it. Like, he's not taking it off the property. He just wants to turn it on and put it on his skin and see what happens.

According to The Internet, the air-only torch he finds at his third construction site scan will heat up to around 1,900 °C, which is a good start. He'll find an oxygen-fed torch later if he doesn't set himself on fire. He'll also do it if he _does_ set himself on fire, because the scientific process just works like that. He doesn't make the rules.

Izuku is very very small, and very very quick; you have to be when you have a friend like Kacchan. He ducks in and out of the shed-like building clutching his prize, hides behind some tarps, and fidgets with it until he can get it to turn on.

Izuku doesn't feel heat like normal people. He doesn't feel the…vibrations? Vibrating molecules? Friction? When molecules go really fast they make friction and that's how burns happen. That doesn't happen to Izuku. People who can make energy have this thing called _single progression molecules_ , which is the same thing hero costumes are made of! They grow fire-making Quirk Skin in a lab to make them, and Izuku was obsessed with this fact for a few months. There are _multiple people_ growing _multiple types of Quirk Skin_ in _multiple_ labs! Kacchan tells him to shut up and stop being gross whenever he brings it up but Izuku can't help it.

Well _anyway,_ it's _important,_ actually. He found out passive Morphics don't exist. You have to intentionally morph into stuff. That's the _point._ Endeavor's face isn't _constantly on fire_ , it's just his hero thing.

Which means Izuku isn't just a Morphic. His existence produces energy. A…Izuku scrambles to stitch all the terms he's read in Books together. R…Reactive Energy quirk? Or something. The point is, _he_ _'s made out of a material that manipulates heat._ And that means he can…he can…erm…

Well, Izuku hadn't gotten past that in his research, but he's sure he'll figure it out by the time he's ten, because he's an experimenter, and he's got a blowtorch right here to help him on his way.

After it runs long enough, Izuku wiggles his fingers in front of the tip of the flame, and then sinks it deeper until he can turn his hand all over in the fire. The heat feels like its curling around his fingers; Izuku thinks he's always warm because there's a shield of temperature stuff that might wrap around him naturally, on account of him being made of weird new skin.

It's not like Weird New Skin is weird, or new. Which is kind of a bummer. Reactive Form is the fancy science term for "people who have skin made out of weird things". It's just that they're not normally _energy_ or _fire_ things. They're usually textures and stuff, or twisting light around.

Izuku's never heard of someone with heat-related _skin_. He hopes they can grow it in a lab.

The fire starts seeping through his Warm, and for the first time in his eight years of life, he experiences _hot_. It sinks into him more than an hour of his hand on a stove iron could ever achieve. His molecules don't do friction, so it mostly just sort of tingles and goes numb. He can actually see his skin vibrating. It's _so cool_.

After a few minutes of this, his skin is starting to glow red, and the texture starts feeling… _weird_. _Too_ numb. Izuku stretches out his palm, and to his awe, the skin breaks and parts into molten slag, with bright glowing yellow lines being pulled open like scars.

He blows on it like you'd blow on a fire, and it erupts into sparks and flickering flame.

He _can_ catch on fire.

He's going to need to figure out a better way to pull it off, though. He'll get back to that!

Using one hand and his thighs to carefully turn the blowtorch off, holding his molten hand up high, Izuku tries to make as many notes about his new condition as he can:

 _\- Not gooey or liquid like actual lava. Kind of stretchy. Melty rubber, maybe._

 _\- Hand works fine._

(Would Kacchan be mad if he saw?)

 _\- Prickles a bit. The parts where he blew on it to make a fire feels extra tingly._

 _\- Vibrating so hard that it_ _'s shaking all the way down his arm. Feels like a massage chair, or a chihuahua._

 _\- Not sure how to get it to cool down._

Izuku stares wide-eyed at his raised arm, actually thinking about the situation for the first time since he decided he needed a blowtorch.

It…it _will_ cool down…

… _Right?_


	2. Psuedoscience Is Not A Guiding Principle

**Experiment Two: Pseudoscience Is Not a Guiding Principle**

* * *

Bakugou Katsuki is a very hot sort of person.

The way flames fly up from his hands, the way it sears, burns, eats up what it touches. Izuku is sometimes dizzy with the overpowering odor it causes, and even that scent is like a blaze. Izuku has never had a concept of 'hot', and he thinks that maybe Kacchan hasn't either, but there are other senses to imply it. To Izuku, who could never feel that kind of temperature change, Kacchan _was_ heat.

Or, he was until Izuku stole a blowtorch and superheated his hands to 1,900°C.

His entire body is jittering now - the weird movement it does to diffuse energy has spread to the rest of him. He shuffles along, hands carefully raised, and the dirt around him ripples with his vibrating limbs. His hands prickle and feel awfully dry. Evaporated sweat? This is not a very good thing to use with Kacchan, then. He'll have to turn it off.

S…Somehow.

He can't give them the torch back, because his hands would melt the thing, and it would probably explode, so he ends up just walking down a back alley and hoping they'll find it eventually.

Around the time his shirt catches fire, he realizes that putting his hands out is going to be a problem. He can't blow on them, because he remembers air makes fire stronger, which is a thing they tried doing to with Kacchan. He can't smother it with water, because there's no way to get to water without setting _way too many things_ on fire.

Izuku entertains pretending to be a villain so the heroes would go after him extra fast, but decides they might take him to jail, so that doesn't really work.

Oh! He knows! He'll _ask_ for water!

Izuku runs out into the street. No one's around, but he can't knock any doors with his hands like this. If his shirt caught fire just by being _close_ to his hands, he could set someone's entire house on fire by touching it directly. That would be bad.

He makes his way down the street, but doesn't see anyone. He'll need to get close to some stores before he starts seeing people walk around, he thinks. Izuku starts running so he can find a store faster.

He spots a convenience store about the same time his shorts catch on fire, at which point he starts desperately waving through the window. Someone comes out to look at him.

"What's wrong with your arms?"

Izuku glances up. The molten slag has spread. He adds another mental note — his body retains any temperature it comes in contact with, which is why his shirt would catch fire just by being on his skin.

"I made it too hot," he explains, "I have to suff…suffocate it so the rest of me doesn't get any hotter."

"You can't turn it off?"

"That's not what my quirk is. Can you hurry? I'm going to be naked soon. And I like these shoes. Uhm…hold on." Izuku pulls his sneakers off and walks forward in just his socks. His lower legs don't feel tingly yet, so he's sure the shoes are fine.

"I'll ask for an ice hero," says the clerk.

"Oh! That's a much better idea, thank you! Do you have some sort of fireproof thing? I'd rather have something melted to me than be naked."

The clerk makes a face, but gets him a fireproof blanket. He can't get close enough to Izuku to wrap it around him, so Izuku has to sit on it and awkwardly pull it over his lap with his toes. It's already bubbling. He outstretches his arms to either side of him.

By the time an ice-quirked hero arrives, the concrete underneath Izuku's hands has begun to yellow and break apart, and the heat has reached his shoulders and neck. His lips and mouth are really, really dry, and the blanket over his lap has long since caught fire, though thankfully it only melted a little bit and he thinks he can peel it off easily enough.

"What kind of quirk is that?" The hero asks, bewildered.

"My dad's quirk was Blazing Stomach," says Izuku, "but I think this one's more like…'Thermometer Magnet'!"

The hero stares.

Izuku's smile trembles, and he glances away. "…Sorry. Is that a stupid name?"

* * *

This whole molten arm thing is not normal, as it turns out.

He has something called a 'Legacy Quirk' — the two quirks that made up his father's quirk had broken up, and Izuku only got half of the mechanics. It's a rare genetic disorder, apparently, occurring most frequently from parents who have one of those split quirks. His dad doesn't have split quirks, though. His grandma had a mild warmth quirk, and his grandpa had an iron stomach. You can't ignite your stomach by making it warm.

Izuku's grandma isn't alive anymore, so he can't prod her on how her quirk _actually_ works. Instead, he gets a bunch of scars all over his arms, a lecture from a hero, and grounded for two weeks.

The hero who saved him, Glacia, had no pity for him. It took about an hour to cool Izuku off, and she had to be careful because apparently, Izuku can also retain absolute _cold_. In the end, she couldn't get his skin to set properly, and he ended up with pale zebra stripes all along his arms and neck. He thinks they look cool, but Glacia and his mom didn't see it that way.

His mom made him promise to never play with that kind of firepower again. He said okay.

He's more interested in the cold now, anyway.

His school has a really, really big freezer. New hypothesis; what happens when he absorbs the temperature of the freezer? He'll just keep being frozen until something warms him up, sure, but what happens to him? His skin accommodated for heat by vibrating a certain way, so will it accommodate for cold the same? His science books say cold molecules move really slow. How will his skin work with that? Can it, if the default quirk he was working with was 'make things warm'?

He wish he could grow his own body parts in a lab. That would make things so much easier.

"What happened to your arms?" Kacchan practically screams into his ear.

Izuku flinches, but recovers quickly. "I melted my arms."

"Gross!" Kacchan laughs.

"How'd you melt them?" Another one of Kacchan's friends asks.

"Blowtorch," Izuku says simply, which makes Kacchan howl with laughter. The teacher yells at him for being disruptive.

In math class, Izuku draws up a temperature map for his quirk. He thinks his melting point is roughly the same as steel, approximately 1,300°C, but his heat tolerance is way higher, and he can safely hit 1,900°C without a problem. Well, he'll vibrate a lot and his flesh will melt, but if he gets help quickly, that only means more scars.

His base temperature is generally around 48°C, a little higher than most kids his age can tolerate, though it's dropped to 40°C ever since Glacia had saved him. Izuku thinks that his natural body temperature is probably around 35°C to 50°C depending on what kind of temperature he last absorbed.

Izuku's pen raps against his notebook. That leaves his lower temperatures, but how on earth is he going to successfully lock himself in a freezer? It's not like ice quirks are common, and Glacia was already mad at him for experimenting.

Kacchan…He thinks Kacchan must have a high tolerance, but he's described things as 'hot' and 'cold' before, so he must be able to feel temperature at least a _little_. Izuku thinks that if he put a blowtorch to Kacchan's hand, he'd burn instead of melt. Actually, Izuku is sort of curious about how Kacchan's body behaves in relation to tension and texture. If he can set off explosions, he can release bursts of tension on his hands, and if his skin is leaking nitro, it must be a specific material.

Izuku whips out his old 'Sidekick Record' and starts jotting down theories. He thinks Kacchan is an example of a perfect fusion, his skin becoming both 'material that can release tension' and 'material that can release nitroglycerin' simultaneously. That's why everyone thinks he's so amazing. That means there's more to Morphic, Energy, and Shape quirks than he realized. If Kacchan got his quirk erased, his skin would no longer be able to output the things it usually can, but would it stymy the explosions or the fuel? Both? Is Kacchan using an energy and Morphic combination, or are they both Morphic?

"What are you mumbling about?" Izuku's seat neighbour asks.

Izuku glances over to him, then back at his notebook. "…Nothing."

After class, rather than follow Kacchan, Izuku wanders around until he finds his history teacher leaving the staff room. Izuku waves wildly at him.

"Sensei! Senseeeiii!"

"…Yes, Midoriya-kun…?"

"Uh, uh," Izuku flips through his notebooks until he finds his train of thought. "Uhhhmmmm I'm experimenting with Kacchan toooo make his quirk stronger and cooler, and I was thinking about how it worked. So I broke it up into bits and, and, and when I look at it, I feel like, it's like he's got a quirk where his body is made out of a material that makes explosions and _also_ nitro? So does that mean he has a Shape quirk? Or is it Morphic, because it's something he has to activate?"

The teacher blinks slowly at him. "Morphic…and…shape, you say."

Izuku nods insistently.

The teacher opens his mouth, closes it, and runs a hand over his face. "…Right, I…Okay. Where'd you hear those terms?"

"I have a billion research-y books on this! I don't know all their titles, though."

"I…Right. Listen, Izuku, how do you think the effects of quirks are produced? Just, any quirk."

"…Pinky toe!"

The teacher's mouth twitches. "No, I mean when people use their quirks, how does it work, you think?"

"Oh…" Izuku blanks. "…Like, Kacchan's…I guess?"

"So what's the difference between a 'morphic' activating their quirk and a 'shape' using a normal part of their body? Imagine someone with a frog quirk. If they stretched their tongue, does this make them a morphic?"

Izuku's brow furrows. "Uhm…No?"

"But people didn't originally understand that. Izuku, what you're using are _colloquialisms_. _Ancient_ ones, in fact. In reality, those with quirks have bodies that accommodate them on some level. Anything less would be a birth defect."

Izuku's mouth hangs open. The teacher raises his eyebrows and nods expectantly.

"B…But…The classes…?"

"The classifications of quirk are Metamorphic, which are severe alterations to the human form, Esper, which are using the mind to induce an effect, and Characteristic, which is what Kacchan and yourself are. Do you understand?"

Izuku rapidly recalculates. This is really taking the fun out of a lot of his theorizing, but it also makes a lot more sense. "I _was_ thinking that Kacchan and me have bodies that kinda work the same-y."

The teacher gives him a relieved smile. "And there you have it!"

Izuku slaps his notebook on the floor and erases a huge chunk of notes, replacing it with the new information. He doesn't want to tear up the paper, so the rest will have to be corrected with white-out. This makes organization sooooo much easier. He's going to spend _all night_ filing all the people he knows until he's _sure_ he's got it right.

So…His mom is an Esper, and he's a Characteristic. Izuku is pretty sure he doesn't have an Esper ability. Kacchan is a combination of two Characteristic quirks. Ahhh, this answers so many questions…He thinks that this better classification must have happened in the past 30 years, way after what they're currently covering in class. He rattles his pen between his teeth. He'll have to ask an older student for their textbook if he wants a true, unbiased, _non_ -colloquial reference. He doesn't know enough kanji or big words to read the non-fiction books in the library.

"…Can you not do that on the floor, Midoriya-kun?"

* * *

Izuku hasn't been _completely_ distracted from finishing off his temperature scale, but he's gotten suuuuper curious about Kacchan, now that he knows that the things they have in common are more different than expected.

He knows Kacchan is probably back at the sand pit, so before leaving school, Izuku runs to the art room and takes one of those little metal paint-spready-things before going off to find him. Kacchan is trying to fly using explosions alone when Izuku arrives. So cool. He'll have to take notes later.

"Kacchan!" Izuku shouts, running towards them all. "Kacchan, I found the perfect test!"

"You don't need to test anything, just make my hands sweaty!" Kacchan snarls.

"No, no, look," Izuku places the paint-spready-thing on the ground and gestures to it. "Heat it up with explosions. Make it like, hot enough to set things on fire!"

"Why the hell should I do that!"

"I wanna see how strong Kacchan is. Pleeeaaase pleasepleasepleaseplea-"

"Alright! Geez!" Kacchan aims his palms at the tool, concentrates, and lets loose screaming _"DIIIIIIIIIIIE DIE DIE DIE!"_

It kicks up a bunch of dirt and rocks, but Izuku does his best to keep his eye on it. Most of Kacchan's explosions are a release of pressure, but nitro is nitro, and the heat slowly climbs. When the metal looks actively red, Kacchan backs off, panting heavily, and Izuku gingerly picks the tool up in his hand. He can't feel how hot it is. It's probably good enough.

And then he slaps the scorching metal against Kacchan's arm.

He's grounded for another two weeks.


	3. Education Is The Key To Success

**Experiment Three: Education Is The Key To Success**

* * *

So, the freezer.

Doing research is a little harder now that he's banned from the computer. Also from Kacchan. And from doing anything without adult supervision. It's fine, and Izuku is grateful that he didn't _scar_ Kacchan or anything. He really didn't expect him to scream like that, but Izuku gathered plenty of data about how Kacchan handles stimulus now. While it didn't injure him at all, it hurt like it should. Kacchan feels regular temperature scales even though it's useless for him to be like that. Izuku supposes that all quirks come with little limitations like this.

Anyway, with that, Izuku figures they're even. Kacchan got away with too much stuff when they were younger.

In the meantime, Izuku flips through his books until he finds entries about the history teacher's terms. His books are old, gotten on a discount at a resale shop, so maybe he should have been more distinguishing? Well, anyway, not a lot of these books have references to that, except as a 'new idea'. Maybe he should take another swing at the library books? He'll be nine soon. He should be smarter by now. Maybe he'll be better at reading them?

"Izuku, get out of there."

Izuku shamefully climbs out of the box freezer under his mother's stern gaze.

He can't go to the library without his mom's supervision, but by the time he's decided he wants to go, his mom has already gotten started on lunch, so Izuku resolves to just take notes on what little information he can find on the _real_ classifications, which is unfortunately 'not much more than the history teacher, actually'. There's two extra ones, though; Projected Effect and Complex Morphic. The book he finds the terms in don't clarify, but he writes them down anyway.

"Hey mom, have you ever heard of Projected Effect or Complex Morphic?"

"Oh, uhm…" His mom pauses in chopping. They're having stew today. "Those are old terms, aren't they? I can't remember what they're for."

"Why's there so many terms about quirks?" Izuku mumbles under his breath.

His mom ruffles his hair. "Well, Izuku, quirks are complicated, and we've had them for a long time! Other complicated things keep getting renames too, you know. Like mental illnesses!"

Izuku decides he's also going to learn everything about mental illnesses. "Okay."

She turns back around to chop up the vegetables for the stew. Izuku folds his arms and rocks in his chair. He's kinda stuck until he can get to the library, huh. He sorted everyone into alignments yesterday, including his mom, and ended up rewriting all his "For the Future" and "Sidekick Record" notebooks to accomodate new data. He coincidentally only has 3 notebooks left. He's going to need more.

Anyway, he's bored now.

"Izuku, _out_ of the freezer!"

* * *

Izuku almost cracks his head open on the counter rocking with excitement as they take his books out. The librarian gives him a concerned look, but he ignores it, excited as he is. Not only books on quirks, but archeology, mental illnesses, and a whole bunch of other fields of study where things change definition, mostly because he still doesn't totally get it yet. He's made sure to get "The Monster Book Of Quirks", and also a book about quirk-based chemicals that Izuku still has a hard time understanding, but should be easy enough to take notes from if he uses The Monster Book Of Quirks.

The moment they're done scanning, he stuffs them all into a bag and clutches onto it like his life depends on it. He bounces around as his mom attempts to guide him through the door.

"Careful," she sighs as he almost walks into the detector.

Izuku is not careful. He's too excited! He's got a huuuuge pool of information to work from! Kacchan will probably stop being mad at him eventually, and when he does, Izuku has so much research to unload on him! He'll make Kacchan's quirk so strong!

He'll make his _own_ quirk strong.

"You sure are researching a lot," his mom notes.

"Knowing more makes me better at growing real fast," Izuku nods.

Izuku is on the watch out for quirks to categorize, now that he's worked through his classmates and also he's banned from the computer. He's trying to do most of them from memory, but it would be really really useful if he could maybe examine their bodies himself, ask questions, that sort of thing. He tries to use advertisements as reminders, but he really doesn't have a full recollection of _every_ hero, which is why he also got a hero catalo- _**ICE QUIRK**_

Izuku drops his bookbag and sprints across the road without even fully reacting, intent on the middle-school girl using an ice quirk to cool off her friend's drink. He trips over the curb, rolls twice, and throws his hands up when he lands, ignoring the stinging of his elbows.

" _Freeze me!"_

She stares at him. Izuku's mom is shouting from across the road.

"Huh?"

"Please! Freeze me solid! If you're capable of absolute zero, that would be ideal!"

"Absolute zero?" She repeats, looking…unhappy, or something close to it. Now that Izuku is looking closely at her, her white hair is mixed in with small sprays of red, vivid enough to be related to a quirk.

"What's your quirk! Does it have anything to do with fire? Can you freeze me? How long would it take?"

"Kid…It's illegal to use quirks like that out in public."

"What is _wrong_ with you?" Her friend interjects.

" _Izuku!"_ Izuku's mom grabs him by the collar and yanks him up. "You can't just _run out on the street_!"

"Ice quirk," Izuku says insistently.

She ignores him, spinning him around and shoving his head down into a bow. "I'm _so_ sorry about my son's behaviour. He's been…very ambitious about research."

"I can take on temperatures, see?" Izuku shows Ice-Quirk Girl the scars all over his arms. "I can superheat my body! But I need to know if it can supercool!"

Ice-Quirk Girl blinks. "Aren't you the kid who set his arms on fire outside a gas station?"

"I just asked the convenience store person for help. Glacia has an ice quirk but I don't think she'll freeze me if I asked."

"Uh, _good?_ That's _dangerous_."

"I don't think that'll stop him," Izuku's mom breathes.

Izuku droops. "You won't freeze me?"

"You should be happy with just the heat. Take better care of yourself! If any of my little brothers _melted their arms off_ , I'd kill them myself."

Izuku shows her his mottled palms. "My arms are right here. Are you joking about killing?"

She gives him a plain look Izuku can't read, and then marches away with a scoff. Her friend leans over to whisper something to her, and they both giggle.

Izuku's mom sighs. "I doubt grounding you will do anything for you, will it."

"I'll get _someone_ to freeze me."

" _Izuku._ "

* * *

Izuku takes another step on his hands, fixated on the book sitting on the floor in front of him. He's decided he wants to train his body and mobility, so he's starting with handstands. First he has to get a good impression of what the balance is like, so he's opted to only move around the house on his hands.

Note-taking is taking _ages_. Science stuff is sooooo hard, and he hates it, and it's all really complicated foreign words he doesn't understand. He has the Monster Book Of Quirks, but its a really big book and assigning each quirk to a category is kind of tedious, especially when it starts reeling off chemicals and roots and stuff. He thinks he'll get a book on Romance languages since words evolving and quirks evolving are _sort of_ similar.

Izuku uses the wall to walk himself to his bookcase, carefully balances with his feet resting against it so he can grab his experiment notebook, and walks back with it in his mouth. His experiment notebook has notes on his own quirk, and a few on Kacchan's. He pages through the book of quirks, looking for something related to temperature.

The ones he can find are…

 **Fire Quirk**

The ability to produce and ignite gases. An Exothermic-Oxidant form. […]

 **Ice Quirk**

The ability to slow molecules in a chain reaction. An Endothermic-Convective form. […]

 **Heater Quirk**

The ability to speed up molecules in a chain reaction. An Exothermic-Convective form. […]

Izuku scratches his hairline irritably. They all seem the same, but they work differently. Izuku doesn't know what these words mean, but he's guessing they describe how the body accommodates for their quirk? Anyway, he's pretty sure the kanji here is 'released heat'…and the other one is 'absorbed heat'…so that means exothermic is making things hotter, and endothermic is taking heat away! He's a _genius_.

Izuku adds 'Exothermic-Oxidant' to his dad, and 'Exothermic-Convective' to himself, and pages through to the physical trait section.

 **Steel Body Quirk**

The ability to harden the body into a metallic material. A Transmorphic-Oxidant-Reinforcement form. […]

 **Hard Body Quirk**

The ability to harden the body into dense keratin. A Transmorphic-Reinforcement form. […]

What the heck is 'Oxidant' doing in 'steel body'?

…Well, whatever. His grandpa had a stomach of steel, so Izuku is adding it to his dad's entry. That makes him _Exothermic-Oxidant_ and _Transmorphic-Oxidant-Reinforcement_? That's only two words in common. Maybe that's why he didn't pass down his whole quirk to Izuku? Because it was too complex?

Izuku thumps his feet against the wall lightly. He can project some of his Warm, enough to make his blankets float and papers ruffle around him, but his quirk isn't 'Heater'. It's definitely not his defining trait. His weird relationship with temperature is way closer. The problem is, his relationship with temperature _isn't in this book_. The three entries he found were the only really close ones.

He flips a chunk of pages over to get to the Esper section. _Their_ 'forms' are way simpler, and even an eight-year-old can get the gist of them. 'Matter', because they can manipulate objects, 'Mind', so they can do things to your mind, and 'Force', which is only on things where you make like barriers and stuff?

Oh, wait.

Izuku goes back to the Characteristic section. _Duh,_ he can cross-reference based on what each quirk does!

Oh, right, and then he can add tags onto each of the heroes and classmates he has notes on! Perfect! By the time he's through with the lot of them, he'll be an _expert_ on quirk dynamics!

Man, these four weeks are going to fly by in no time.

"Izuku, what are you doing?"

Izuku looks up at his mom's upside-down figure. "I'm balance-training."

"Well balance-train your way into the kitchen. It's dinner time."

Izuku tilts forward, careful to avoid stepping on the ring of books around him. "'Kay!"

* * *

Fuyumi drops her bag with a sigh. She just wants the semester to _end_ already, but she also doesn't want to spend more time home than she has to. Running away sounds awfully appealing, right about now, but her siblings would freak, and her dad will drag her back home and lecture her about 'image' for 5 million years.

She removes her shoes and socks and feels the cool tile of the dojo against her toes. She's not going into heroism, but Todoroki Enji has enemies, and anyone can take a crack at his kids. Fuyumi gets the impression that the real problem he has with that is the bad press it would give him. _Oh no, is Endeavor really that powerful of a hero, if he can't even protect his own spawn?_

She considers faking her own death just for the privilege of seeing it. The untimely downfall of the #2 hero!

But no. Responsibilities. Fuyumi bows at her instructor, and they begin the sparring session.

Two of her brothers get to train after her, but her youngest sibling is locked away with his dad, getting some one-on-one hero training. She's only seen his face, what, three times? Ever? He's sort of like a ghost. Fuyumi doesn't think he'd care much if she faked her death. Maybe she can make it so her closest siblings know and no one else?

It's not like her mother would get any worse. She's already crazy.

"Keep your mind on the match, Fuyumi-kun," her instructor says with a glacial edge.

"Yes sir," Fuyumi replies briskly.

"Is there anything weighing your mind?"

Her mouth pulls. "No," she lies.

"Nothing happened recently?"

"I…" She takes a step back and thinks of something believable. "…A kid ran up to me asking me to freeze him, earlier, that's all."

The teacher blinks, looking just as surprised as she felt. "To _freeze_ him?"

"He's the kid that set himself on fire in front of the convenience store. Apparently he's trying to test out his quirk, and he just _melted_ himself. There were pictures and everything online, right, you could see he was kinda like, lava-flesh," she shuffles nervously, "and he wants to test it the other way now. So he sees me chill my drink, and starts screaming at me about freezing him. Weird kid."

"I wish _any_ of my students had that level of enthusiasm," the instructor says dryly.

Fuyumi shrugs and gets back into position.

"Yeah. Well. That's what was on my mind."

Maybe she can make a new life in America. That'd be nice.


	4. Resolve Is Cultivated Slowly

**Experiment Four: Resolve Is Cultivated Slowly**

* * *

Izuku has a rough understanding of categories, now.

Exothermic is a release of energy - not necessarily heat, because it shows up on light-based quirks sometimes. Izuku thinks Kacchan is one of these, because of the release-explosion part of his quirk. That's energy, right? Probably. It's sort of like how if you rub your hands together they get warmer, but as a quirk, Izuku thinks.

Endothermic is…Well Izuku isn't sure what Endothermic is, but it sounds important. Freezing stuff seems 'cold', like the Ice Quirk said, but turning liquid things into hard things is Exothermic, and isn't _water_ a liquid thing, which becomes a solid thing (ice) when it's _cold_ , which is _Endothermic_? Also, melting objects or turning into smoke have 'Endothermic' tags too. _Steam_ quirks are Endothermic, and isn't steam supposed to be _hot_? It just _doesn't make sense._

He had to look up Oxidant in a book about science, and as it turns out, it means things that are made up of oxygen, or something? He saw the word 'oxygen', and he's seen science posters. He's guessing that how it works.

Convective is spreading of temperature, so whatever Izuku has, it's _definitely_ convective.

There's other words like Conductive which mean like 5 billion things and Transmorphic which is changing your body's traits which also means like 5 billion things, but Izuku has a rough handle on it, at least enough to assign them to all the quirks he's recorded so far.

That isn't to say he's _perfect_ at it. There's a kid in his class that can stretch his eyeballs right out of his head, and Izuku has no idea what the heck he is, and his books are all way too complicated for him to figure out, even when he uses a dictionary. It's reaaaally boring and he hates it so he's just not bothering right now. Eyeball kid can be an enigma.

So Izuku is Exothermic-Convective, which means he can release energy (puffs of warm air) and temperature spreads within him? Past him? Something like that. So he needs to find a term which says something about endurance…There's 'Rubber Body Quirk', which is a Metamorphic quirk, and Metamorphic quirks have barely _any_ descriptions on them. They're all 'Substance' and 'Fauna' and whatever.

The Esper section is also like that. Characteristics probably get more categorization because they're so much more complex, and interact in weird ways, like Kacchan's super-awesome amazing ener— er, _Exothermic_ quirk, which is like, perfectly designed, like his parents married for the sake of the most perfect-est quirk baby ever. The more Izuku finds out about quirks, the more amazing Kacchan is.

"Midoriya-kun, aren't you going to play outside?"

Izuku slides a hand over so he can turn while still balanced on top of his desk. It's his homeroom teacher, peaking into the class. Izuku can't wave at his teacher because he'll definitely fall if he lifts either of his hands, but he smiles.

"I'm okay! I'm balance-training!"

"What are you going to do if you fall?"

"Dunno!" Izuku turns back to his notebook. He wishes he did this against a wall. He can't write and stand on his hands at the same time. He's wobbling enough as it is, and he had to rest his heels on his butt a while ago just to stay upright.

"Aren't you going to play with your friends? Like Bakugou-kun?"

"I'm grounded from talking to him, and I think he's still mad at me for burning him." Not that Izuku understands why. Kacchan took on middle-schoolers and they punched him and kicked him a lot and he was _fine_. Izuku has been punched and kicked a lot (by Kacchan) and it hurts a _lot_. There's no way hot metal could be worse. Izuku almost melted his flesh off and he turned out alright.

He releases another puff of air to flip the page. It takes about four tries before he gets it right, and he wobbles dangerously with the strain of it. The teacher leaves the class. Izuku's fingers tap against the desk.

Kacchan needs him, anyway. Izuku is his most useful friend. He'd wait for him.

* * *

"Kyaaa, save me!" Izuku's mom cries, splaying herself over the floor.

"Never fear! _I_ am here!" Izuku sprints towards the couch and jumps as high as he can, using a short burst of air to throw his balance into a full flip. He lands on the coffee table and strikes a heroic pose.

"My hero!" She cries.

Izuku whips the blanket off her back. "A perfect rescue! Well? How'd I do?"

"Perfect!" She ruffles Izuku's hair. "That's a lot of progress for just a week and a half! Are you going to do gym courses?"

"I think so?" Izuku tilts forward to stand on his hands again. "I can only land properly if I do a flip. When I just stand in place I just wobble and fall over."

"It's normal for a boy your age to be bad at balancing."

"But how am I supposed to get around uneven ground and do upper-body strength! With my arms!" Izuku flexes and keeps himself upright by leaning a foot against the wall.

"What about pull-ups?"

"About the wha-?"

"Like so!" His mom grabs him by the waist and hoists him in the air, making him squeal. She drops him just behind the couch, and holds his legs over the edge. "It's a tough-guy training regimen! Try to pull your upper body up!"

Izuku lifts his neck, but finds the rest of him too heavy. He uses his arms to push himself up off the back of the couch to get some leeway, but he barely manages half a second before dropping and bonking his head.

"I think I need more balance training before I'm strong enough…" Izuku mutters.

"Hmm…I think so too. Too much training in elementary school will stunt your growth."

"Yeah! And then I'll be the strongest middle-schooler!" Izuku wriggles out of his mom's hands and flips backwards into a crouch. He strikes another pose. "To be a hero!"

"A splendid hero!" His mom claps.

Heroes have to graduate high school before they get their license, don't they? So Izuku only has a limited amount of time to be strong enough to be a hero. He only has a limited time to be able to get into the best school with Kacchan. If he doesn't, how will Kacchan be the best hero?

That's right. Izuku is smart and soon he'll be strong, and he definitely won't be left behind. It's not possible!

"S…Super Thermal Man!"

"Oohhh!"

"Thermal Might!"

"How catchy!"

What will Kacchan's name be?

"Hearth man!"

When he gets his license, what will _his_ be?

* * *

"Don't you want to give up on this already?"

The dojo is frigid at this point. When their bare feet part from the ground, they leave prints in a thick layer of frost.

"Aren't you ashamed of your father seeing you in this state?"

Todoroki Shouto takes a deep breath of air and feels nothing. The skin under his bandage twitches. Is his father watching? He doesn't usually supervise their morning practice. His numb fingers twitch with hesitation.

"Use your fire. I know you're capable of it."

"I don't want to."

"If you want to be a hero-"

What's so good about heroism? His _father_ is a hero, and he's-

The skin under his bandage twitches again.

"…I'll use it against him," Shouto mumbles.

"If you want to learn how to use your quirk effectively, you need to put your _all_ into training."

"You'll get burnt," Shouto says, louder this time.

"I can protect myself."

"Not perfectly." Realizing the extent of the situation, Shouto slaps his hand over the bandages covering the left side of his face. "I'm not using my quirk unless I _know_ you won't be burnt."

"Shouto-kun. Your quirk is too radical to depend on that scale of absolutes. Even if I found someone who could tolerate your fire, they'd have to adhere to your constant training regimen, not to mention the safety risk when it comes to your ice. You have to trust us to be able to protect ourselves."

Shouto takes two steps back and scowls fiercely, already latching on the tiny sliver of opportunity with bull-headed determination. _"Then I won't do it!"_

" _Plea-"_

Shouto shoots up a wall of ice between him and his mentor. Like this, he'll only have to use his fire quirk once a day! If he could phase it out completely…If he could throw at least that in his father's face…

He flattens himself against the wall and holds his breath.

"…You really are a prodigy." His mentor raps his knuckles against the wall of ice. "I doubt any of your siblings could manage this much."

Shouto lets out a steamy cloud of breath, feeling the urge to run out of the room outright. His father wouldn't like that, though. The beating he'd get wouldn't be worth it.

"Shouto-kun." His mentor circles around the wall and looks at him with a gaze that makes Shouto's stomach churn. "I'll bring a training partner up to your standards on Monday."

The sliver of opportunity breaks apart into the tiny snowflakes settled at his feet.

All he can do is nod.


	5. Strength Begets Strength

**Experiment Five: Strength Begets Strength**

* * *

The fourth and final week comes in all too soon, falling unceremoniously into Izuku's haze of research and constant handstands.

Izuku tries to catch Kacchan's eye every now and then, excited at the prospect of sharing everything with him now that his Kacchan Ban is almost up. Kacchan doesn't look at him much, but that's okay. He hasn't had to think about Izuku for over a month! Izuku was only looking because he wants to see how Kacchan was doing, anyway.

They're learning about quirks in school, now, and the homeroom teacher is using a bunch of extra terminology when he talks about applying to good middle and high schools. Terminology he doesn't recognize.

He's starting to get a little frazzled by expanding definitions. While Morphic, Reactive, and Shape are _archaic_ , they're also the root categories for anything not related to science, because society is based on old words, regardless of how accurate they are. No one cares about _scientific terminology_ when they just want to know how your quirk affects your day-to-day life. This is troublesome, because Izuku was really getting into Denying The Old World and Bringing The Age Of Science or…or something. Whatever Izuku was looking forward to, it was vaguely awesome and smart-sounding.

Anyway, Espers and certain Characteristics are basically the same thing when it comes to gainful employment and it's soooooo annoyiiiiiiiing.

Izuku, in a fit of frustration, has created a chart so he doesn't accidentally use the wrong words.

 **Reactive | Shape | Morphic**

Old quirk classes based on what they do.

 **Emission | Mutation | Transformation**

New quirk classes based on how they affect you.

 **Esper | Characteristic | Metamorphic**

Scientific quirk classes based on how quirk types are related.

This is a lot to remember. If Izuku brought this up with Kacchan, Kacchan would probably blow up his notes in disgust. Izuku relates deeply with and respects this imaginary Kacchan's decisions. If he ever becomes the boss of quirks, the first thing Izuku will do is make it so only one version of quirk categories exist and that one is the smartest one.

Izuku will be…the Quirk Hero, Science Man.

Yeah. _Awesome._

He tries to catch Kacchan's eye. Kacchan doesn't look back.

…The field of mental illness is really fraught, too, with Mind-Split Disease becoming Integration Disorder, a weird kerfluffle where a bunch of disorders sort of collapsed into each other, some falling into personality disorders while others becoming a part of a spectrum, and a lot of in-fighting. Izuku makes sure to pay extra attention; when he grows up to become Science Man, he'll have to fight people with the power of really hard-to-read essays as well, and he needs to crib notes.

 _Societal Perception_ comes up a lot. Izuku doesn't really like this, because both the 'social life' quirk classes and the 'scientific research' quirk classes are pretty neutral and self-descriptive. But then some symptoms of certain mental illnesses show up in _other_ mental illnesses really often, and some of these fights talk about _misdiagnosis_ and _treating both_.

That's right! It's easier to learn more about your own quirk if you just think of it in terms of the scientific way, and people not using the _scientific_ way more means they might misinterpret their quirk!

For instance, Izuku was frustrated with archaic quirk terminology because it was too inflexible for more nuanced quirks. But the _new_ version is more obvious: he's a mutation! He's made of warm! But that sort of makes Izuku think that he has a _second_ quirk integrated into that, the one that makes 'emissions'. This isn't true; Izuku's quirk is just his grandma's and no one else's.

He's written his first-ever Science Essay to describe the socials…socializing…

Izuku checks his notes again.

The _sociological implications_ (he's stolen this word from another science person's essay) of rigid categories! Why, if Izuku didn't know any better, he'd assume that his quirk was actually _weak_ and _useless_ , and it's only thanks to his _scientific mind_ that _instinctively thought about science_ that he revealed that this thought was a fake thing and his quirk is actually super cool!

Kacchan still isn't looking at Izuku. Is he ignoring him?

Anyway, maybe Kacchan will be limited by 'it's just a good Emission quirk'. If he's going to be super strong, he has to be more flexible. While Izuku's quirk is simply flexible, Kacchan is a combination of two quirks, and needs to think of it like that if he's going to be the #1 hero like All Might is.

The bell rings. Kacchan takes off. Izuku stares at his desk for a full minute before he decides he's had enough of theory.

There's no one in the infirmary when Izuku peeks inside. The school nurse typically leaves for lunch, which gives him about ten minutes to find what he needs. Mainly, a minimum of two glass containers, maybe a syringe if he's lucky.

The cabinet is unlocked, and Izuku drags a chair over to reach. There's a glass jar of tongue depressors, which Izuku empties into the plastic container of tongue depressors on the nurse's desk, and he does the same for the cotton swabs. He has to do some digging for a clean syringe, hidden in a cardboard box on the topmost shelf. There's a few more in there, so the nurse shouldn't notice if it's missing.

Oh, right, didn't his doctor do a few other things when giving him his shots? Let's see…a tie around his arms so his veins would show up, and theeen something to absorb all the blood.

Izuku grabs a fistful of cotton swabs, a few disinfectent swabs, and tears off a long strip of rubber from a roll. There! Syringe safety.

…Or is it?

He quickly shuts the cabinet and slips out of the nurse's office, trying to look as inconspicuous as possible as he heads up to the computer lab, where they teach you how computers work. There's a teacher here, because lots of kids like Izuku can't afford their own smartphone.

Izuku quietly logs in as a guest and looks up 'how to use a syringe'.

There. _That_ _'s_ syringe safety!

…Probably not computer safety, though?

He opens four more tabs with searches like _'how to hide a body'_ , _'blood splatter patterns',_ and _'best murder mystery plots'_.

 _Computer safety!_

Now that that's taken care of…

' _Freezing point of blood', 'what happens when you heat blood'._

* * *

Theory is all well and good, but theory doesn't matter unless you can convert it into fact.

For example, Izuku has a _theory_ about…

Izuku flips through his science book's introduction pages again.

…He's got a _hypothesis_ about Exothermic and Endothermic abilities, but is true? He can only test it to find out!

(This has the added benefit of being easier to do than finding someone to freeze him solid.)

First, Izuku carefully extracts his blood. Then, he wipes out the glass jars and puts in one blood sample each. He almost drops them both from the force of his dizzy spell when he tries to get up, but he gets over it! Next, he digs through his closet for his science kit he got for his sixth birthday. He carefully pours half of the blood from one jar into the flask, while the other serving of blood gets split into a tiny sample jar. The glass containers and the sample jar get put in the fridge and the freezer respectively, tucked away out of sight.

Next, he studies the blood itself under a microscope, and draws a sample of it in his book, since he can't exactly take a picture of it. They look like normal blood cells, spaced apart decently. He makes a note of this, even though that's pretty obvious, and washes off the slate in the bathroom sink. He makes sure to wipe the washed slate with a disinfectant wipe as well, just in case he needs it later.

Next, he sets the corked flask in the toaster oven. He had to switch containers because he wasn't sure if you can put the jar in the toaster oven or not. He also puts two slices of bread in so it's not as suspicious. He decides he won't eat them, just in case. The toaster oven is left on low heat.

He does his homework at the table for two hours while he waits. His mom comes home, but doesn't notice the toaster oven is on.

When he takes the flask out of the toaster oven, the toast is dark blackish-brown and gross-looking. That goes in the trash.

According to his research, the average person's blood will congeal under high temperatures.

His blood isn't congealed, but it is filling up more of the flask than it did before. He writes this down. When he sloshes it around, it goes super fast. When he lets it sit, the surface never flattens out, instead looking sort of rough. Izuku is guessing this is a tiny version of the way his body vibrated when superheated. Something about pressure and not turning into steam, maybe? This gets written down too.

He takes the small sample jar out of the freezer. The blood isn't frozen, but it looks like there's less than he started with. Strange. It's very still, though. This all gets written down.

Neither of these reactions are in line with the average human body.

Izuku's body is exothermic and endothermic at the same time, but can only _emit_ warm energy. He's not made of warm so much as immune to temperature changes that would make him _less_ warm.

This is probably why he can't feel temperature at all; his body is built around changing to match whatever temperature it exists in.

But if that's the case, why can he release bursts of hot air, every now and then?

Only one way to find out.

"Mom, I'm going to do a scientific experiment and I want you to supervise me!"

His mom looks up from her cross-stitching. "And what's that?"

"I'm going to release hot air constantly for the next uhhhh hour!" He flops down on the couch and starts emitting, with his notebook by his head. "Watch the clock, please!"

Izuku wakes up the next morning to a warbling shriek.

He whips his blanket off and tumbles into the hall. "I can explain!"

His mom isn't looking in the fridge, though; she's looking at the letter in her hand. Izuku slaps his hands over his mouth and curls up into a ball, waiting for her actual reason for wailing.

"…Izuku," she says slowly, beginning an anxious pace, "Izuku, you…they want you to be a p-p-p-playmate…"

"Someone wants to play with me?" Izuku springs up. "Who?"

"They-They need someone to train with their son while he's being tutored…"

"Lemme see!" Izuku tries to snatch the letter out of his mom's hand.

"Izuku- Izuku, don't." She chews on her lip as she reads it over. "This is…A lot of money."

"Who wants to play with me? Do I still have to wait until I'm not grounded anymore?" Izuku bounces in place.

"… _Well_."

* * *

Shouto tries his best not to fidget.

They're having an official meeting with his new… _training partner_ today, which is stressful enough as it is, but he has to welcome his new partner with the rest of his family. His father stands at his side, while is siblings are sitting along the wall, whispering amongst each other. Shouto's legs are going numb from his seiza, but he doesn't dare move.

He's never seen his siblings up close. The sister is bigger than he expected, and might even be the eldest. The brother closest to him has so much product in his hair that Shouto wonders if his whole head would combust if a fire was put to it. He has red in his hair too, around the baby hairs at his nape — could he ignite himself? All Shouto knows about them is that their quirks aren't to his father's expectations, so…

The door clicks. Shouto flinches.

First comes in the tutor, who looks to the sister, who Shouto knows only has an ice quirk.

Behind him, comes in a slight woman with swamp-coloured hair, clutching the hand of a wide-eyed boy with a wind-tunnel tangle of curly hair the same colour as his mother's. He's holding a thermos.

They sit in front of Shouto and his father, both in seiza as well.

"It's a great honour for you to be interested in my son," the woman says weakly.

Shouto gives the boy a doubtful look. He looks the same age as Shouto. Is _he_ supposed to be Shouto's training partner?

"I've heard your son can handle great deals of stress to his body's temperature," Shouto's father growls.

"Y-Yes, he's a—"

"My body is exothermic and endothermic," the boy interrupts, holdings an arm out. Rings of scars stretch out from underneath his half-sleeves. They look more like stretch marks than lacerations. "My body is designed to survive severe temperatures."

"Then you won't mind if I test it."

The boy blinks his big green eyes, not shaken at all, even if he holds himself a little stiffly. "My melting point is around 1,300°C."

Shouto's father stands. Shouto holds his breath as the boy hands his mother his thermos and folds his hands politely in his lap while she steps out of range. He doesn't look like he finds Shouto's father scary at all.

Shouto's father places a massive hand onto the boy's head.

"Can you tell me if it's too much?"

"No," says the boy, "I probably won't be able to feel it until it's hot enough to leave scars."

Shouto's father grins, and blasts him with a wave of heat that prickles through even Shouto's endurance. Within seconds, the boy's clothes peel away, and the flames pour off the surface of his skin like a waterfall. The boy just closes his eyes and lets it happen.

After a few moments, the boy opens them again. "Oh. It's warm."

 _How deep is his tolerance?_ There's no way Shouto would be able to take that much direct fire, and it _still_ seems like it's not enough.

Finally, Shouto's father removes his hand, and he shakes off the ash that clung to it. The boy's pants burn up too, but his underwear shines. Probably fireproof. Shouto wonders, deliriously, if he wears the same kind Shouto does.

"Shouto."

Shouto flinches.

"Ice him."

"It's dangerous to go from extreme heat to extreme col—" The boy tries to start.

"You're to train with someone who's quirk deals in those extremes. If you can't take the cold after that, you're not good enough," Shouto's father growls. "Shoto. _Ice him_."

Shouto gets up with legs that barely manage to hold him upright. The boy's mother looks scared for him. He's wracked with a sudden flashback, of him on floorboards just like these ones, and his own mother begging for his father to stop.

The boy looks Shouto directly in the eye and says "Do it. Absolute zero, if you can."

" _Izuku,"_ the woman says sharply.

"It's fine." The boy walks over to her, trailing smoking khakis, and holds his hand out for the thermos. She gives it to him with trembling hands. He unscrews the cap, and out tumbles out a small glass jar full of red liquid. He presses it against the surface of his forehead, and the contents slosh violently. The glass makes a dangerous-sounding noise.

He walks back to Shouto and passes him the container.

"Freeze it."

Shouto stares at it, and then up at the boy, who is fixing him with a stare intense enough to make Shouto shy away. Gently, he takes the jar. He's about to freeze it when the boy cups the backs of his hands tightly. Shouto whips his head up again, nervous at someone being this close to his quirk. The scars are uncomfortable against his skin.

"Cover your palms with something. The glass is going to explode."

"What's in the jar?" Shouto's father asks.

"A sample." The boy turns his arm to show the melted band-aid plastered to his arm. The cotton swab underneath it is a blackened, glowing husk. The boy's mother seems to see it for the first time.

"Izuku, did you ask the school nurse to _draw your blood for you_?"

The boy looks at her and is quiet several seconds longer than necessary. "…Yes."

Shouto looks down at the jar again. It's really, really hot. Carefully, he spins an egg of ice, with its strongest points at his stomach and palms. "If it's going to explode, step back."

The boy — Izuku? — obeys.

Shouto can't make a lot of ice, but lowering temperatures isn't exactly _hard_. With a deep breath, he clutches his ice egg and fills it with the lowest temperature he's physically capable of.

The glass shatters, and punctures the egg with the force of it. Only one shard actually gets out, though, and he barely feels it. The rest of the…the blood is stuck in solid ice.

Or at least it seems that way, until the cracks caused by the glass are filled with dark, reddish-brown liquid.

"…It's not freezing," Shouto gasps.

"See? Try it." Izuku holds out his bare arm. Shouto looks up and flinches. The scars aren't just on his arms; they form a thick, cordy lace all the way up his shoulders to his neck, where they thin out into small cracks just underneath his jawbone. Whatever happened to his skin looks like it should have killed him.

"Are those from a fire quirk?" Shouto asks quietly.

"No," says Izuku. "My body absorbs temperatures too quickly. I put my hand under a blowtorch for a few minutes and it spread."

One of Shouto's brothers — the white-haired one with a bunch of product in his hair — snorts out loud.

"It was all over the internet," the sister tells him, only barely loud enough for Shouto to hear her.

Shouto holds out a hesitant right hand. Izuku takes it and presses it against his forehead. It's hot, almost painfully so, and Shouto is shocked Izuku hasn't reached his melting point yet.

He takes a big breath, squeezes his eyes shut, and releases as much cold as he can.

Izuku gasps, and shudders. Shouto is met with a burst of warm air, and then a cloud of steam that makes Shouto's clothes cling to him like sweat. Izuku stays otherwise still, letting the wall of ice slowly encase him. When it reaches his toes, Izuku looks like a chunky ice sculpture.

Shouto takes a few steps back.

The ice cracks clean in two.

Everyone watches as the ice coffin cracks into thick pieces that crumble off him. When his head is free, Izuku pulls his torso back, and releases a burst of balmy air, nowhere near as warm as the last burst was, but after a minute of pressure against the ice, it's enough to weaken it enough to wrench himself free.

Then he stumbles forward and collapses to the ground, snoring softly.

There's a heavy silence.

"…Did he _fall asleep_?" The sister asks.

Shouto takes another two steps back, but is stopped with his father's hand on his back.

"Are you satisfied, now?"

Shouto opens his mouth, closes it, and finds that he has nothing left to say. He can't complain. Izuku is theoretically perfect. So he nods.

Shouto's father steps up to Izuku and his mother, who is gently trying to shake him awake.

"Midoriya Inko. We've decided to take your son into Shouto's study program."

Shouto closes his eyes and clenches his fists. His bandage feels soggy from the steam.

With a startled huff, Midoriya Izuku wakes up.

"Th…Thank you…Todoroki-san."

* * *

 **Notes:**

 _Some extra context:_

 _-Izuku DOES have a default temperature baked into him, and his body naturally tries to acclimate himself back to that default temperature. If you baked him up to 900 celcius and then left him in a hot room, he'd still return to 55-60 celcius by the end of the day. Since his natural temperature is decently high, it's easier for him to warm up than it is for him to cool down. This is generally what Izuku means when he perceives his body to be 'made of warm'._

 _-Izuku can't produce cold exhaust. More detail on that later._

 _-Shouto isn't capable of absolute zero, which is good, because even if Izuku could offset it within seconds with temperature equalization, he would die_

 _-Izuku's brain shares his temperature tolerance, but it can't change states, so if it hit his melting point, that would also kill him. Enji is an irresponsible fuck, surprising no one_


	6. Consideration Is The Ultimate Support

**Experiment Six: Consideration Is The Ultimate Support**

* * *

"K…Kacchan."

Izuku flinches as Kacchan looks up at him, and clutches his notebook closer to his chest. He shrivels when he's not given any welcoming gestures.

"Uhm…I'm not grounded anymore."

"Huh? So you'll get to come out with us again?"

Izuku smiles, but then it trembles and breaks down when he realizes the problem. "…U-Uhm…every other day?"

"Whaddaya _mean_ , every other day?" Kacchan makes a little huff of realization. "You got cram school now?"

"H-Huh?"

"Yeah," another one of Kacchan's friends says, "a bunch of kids are starting cram school early to get into good middle schools."

Kacchan looks only a little curious. Izuku jumps on the tepid reaction. "Yeah. I have cram school now. So I can only hang out with you every other day…sorry."

Can you cram for physical aptitude? If you're a hero, probably, right? This isn't technically a lie. And everyone knows how cram school goes. Cram school is normal. It's so normal that even Kacchan knows he can't do anything about it. Izuku doesn't have to explain himself. It's self-explanatory! That's why Izuku doesn't have to tell Kacchan anything.

What if Kacchan was jealous? Izuku is really helpful. He's the perfect sidekick, designed to work perfectly with Kacchan, but Shouto-san has a tooootally different quirk, and…well to be honest, Kacchan is really kind of a huge jerk! He'd be mad at Shouto-san because he'd be so jealous, but then scream at Izuku. It'd be so annoying! He's not even allowed to talk with Shouto-san, his mom told him not to, so it's way different than Kacchan. It's really stiff and boring, unlike going to the sand pit, which is fun and interesting.

Yeah. Good thing he's not saying anything. What a pain that would be.

Izuku stares at his notebook, grasping for something that could distract them, and make everything feel just like it did before Izuku was grounded.

"…I'm free today though!"

"Fine."

"…And I'm sorry I burned you."

Kacchan makes a growling noise. "You just surprised me, is all. If I suddenly punched you in the back of the head, you'd freak way more than if you knew it were coming, right? It doesn't matter."

Izuku beams. "R…Right…I'll ask you next time!"

"…So?" Kacchan tilts his head.

"S…So…?"

"Uh, you did it because you were _learning things_ , right? What'd you learn?"

Izuku smiles so wide his cheeks hurt and opens up his notebook.

* * *

"Now, Izuku, I know you're exci-" Izuku's mom wobbles with the force of his bouncing.

"It's _Endeavor_ _'s_ house!"

"Y-Yes, and you behaved yourself _so_ well, and I'm proud of you, but-"

"And I'm going to play with a quirk just like mine!"

His mom pulls him close and spins him around so he's looking at her. "Izuku. You're not playing. You're training."

Izuku's eyes skate past her face. "It's the same thing."

"No, it- not _exactly_. Izuku, when you're training, you have to follow a bunch of rules. And you have to do them even if you don't like it. That doesn't mean it can't be fun, but it's…it's different."

Izuku pauses, and then continues bouncing on his heels. "Okay."

His mom smiles. "Good! So, today's rules are the same as they were when you met Endeavor—"

"—Calm face and can't talk for a long time—"

"Okay, but you might be a little impulsive because he's the same age, but we're going to need stricter rules, okay?"

"Okay!"

"Well…" She stands, takes Izuku's hand, and they continue their way down the road to the Todoroki household. "You can't ask any intrusive questions, not even about his bandage. You have to be quiet unless you think it's useful to them or you need help. You have to wait by the gate the moment your lesson is over. Don't take any invitations from them, unless one of the adults says it's okay. If an adult asks you to do anything that isn't training, you tell me right away."

Izuku bobs back and forth. "'Kay!"

"Right. I think that's a good start. Right…Oh, Izuku, I'm so proud of you. I know you'll make the best of this." She squeezes Izuku's hand tightly. Izuku grins into her wrist and clutches tight the entire walk to the Todoroki household.

Instead of going to the main hall, they circle the building along the engawa to a smaller dojo attached to it. Izuku has to fight to keep still, but his mom lets him continue to throw his head back and forth. He manages to keep still when the door slides open, not wanting to look to excited, because Kacchan says it's 'uncool'.

Endeavor's son, Shouto-san, stands inside, next to their tutor. The dojo is made of dark wood, with windows peeking out at the top, and the box made of white lines is ringed by humidifiers, but none of them seem to be on. Izuku crouches and runs his hand over what at first glance looks like wax. The surface is far too textured, more like rubber grain, and the colour around thicker edges turns green rather than yellow.

"Izuku," his mom whispers.

"It's covered in an insulator," Izuku explains, "to keep it from damaging the building."

"Your son is quite intelligent, I've noticed."

"Yes, he's my little genius!" His mom laughs and hoists him back to his feet. Izuku looks around, and his gaze fixes on the windows. The surface looks uneven. He moves to climb up and check, but his mom is already steering him forward, apparently to receive some clothing. Izuku obediently holds out his hands to take it, deciding the window can wait for later.

"These robes are insulated just as the surfaces are, and you'll be training in them."

"Okay." Izuku unfolds the shirt with one arm. "Are they made from the same material as my underwear?"

"No. Your underwear melts a bit under extreme temperatures, yes? This is much more resistant."

"What materials?"

"Izuku," his mom whispers.

Oh. Right. He should only talk if he needs help or if he can help them. He can easily figure it out for himself if he just takes a sample home.

"I'll get changed," Izuku says, instead of anything he's not supposed to say, which is apparently a lot.

Shouto-san is already in his robes, so they were probably waiting on him before getting started. Izuku walks briskly past Shouto-san to the rooms beyond, and struggles to squirm out of his clothes while the tutor and his mom talk. He almost walks out with the robe's shirt on backwards, but manages to correct it just before he comes out into the hall.

"Excellent, Izuku-kun!" The tutor claps. "You're ready, then?"

"Yes."

"Your mother is going to watch your first session if that's alright with you."

"Yes." Now his mom gets to see his quirk in action!

"You're a little behind, so I'll be training you on Shouto-kun's kata."

Kata? Like martial arts moves? Is Izuku going to learn martial arts? _Wow!_

He carefully schools his face and stands next to Shouto-san, who is kind of staring now. Izuku bows at him to be polite. People like Kacchan love it when people tell him that he's super amazing and they want to hang out with him, but people like Shouto-san are harder for Izuku to understand, and are as a result extremely terrifying.

The tutor shows him all the kata, which are like lessons about reflexes. Izuku knows nothing about physical reflexes, so he's going to have to learn everything about it before their next lesson. No quirks are involved, which Izuku is disappointed by, but his mom is here, so it's not all bad. He tries not to act up, usually by thinking what Kacchan would do, and then how _his_ mom would yell at him for it. It's a good model, Izuku thinks.

Shouto-san doesn't say anything to him. That's disappointing.

When they're done, Izuku gets changed first. His mom takes him by the hand to leave. Shouto-san watches them go, but stays quiet. Izuku hopes they can be friends eventually.

Let's see…tomorrow is Kacchan day, and then after that, probably more kata…Can he squeeze in research on muscle functions somewhere in there?

* * *

Shouto's new training partner stares a lot.

His eyes are constantly moving around, mostly skimming over different parts of Shouto's body. He makes Shouto feel like he's underneath a microscope, which he's used to, but it's not as uncomfortable when Izuku does it. It might be because Izuku doesn't seem to expect anything from him; he doesn't even ask questions about the bandage over his eye, which none of Shouto's classmates could resist doing.

Their tutor has to go over stretches and kata slowly with Izuku to get him up to speed, especially when their first session reveals how clumsy and slow to follow he really is. Shouto doesn't mind it much; it gives him a break from the constant back-and-forth quirk training between his tutor and his father, which he hates.

It's only toward the end of their second week that Shouto is pushed to use his quirk against Izuku. His tutor expects him to use his fire without complaints, but Shouto disagrees.

He throws up his right side, and a wall of ice flows out from him. Izuku dances around it, but rather than avoiding the next wave, he jumps back on the ice that Shouto had just thrown up and scrambles up it. It makes him harder to attack with the ice waves he's used to making.

Shouto's tutor looks at him.

Whatever. Izuku seems used to heat anyway.

Shouto switches hands, sending off a wave of fire. The ice underneath Izuku shatters, and—

Izuku is engulfed in an explosion.

Shouto flinches back as half the dojo goes up in flames. His tutor leaps to hold him back, and Shouto tentatively throws out a layer of ice to smother it, only to let out a startled shriek as it all explodes _again_. Ashamed now, Shouto shrinks behind his tutor, who gathers the air from the humidifiers using his quirk and uses it to spray the fire into submission.

Izuku emerges unscathed, but fingering his ears like they're ringing. He wanders over to a spot of water outside of the scope of their tutor's water spray, dips his finger in, and tastes it. After a moment, he gives the fire a suspicious look.

"Well, that was, er, unexpected to be sure," the tutor begins nervously.

"Not really," says Izuku. Then, to Shouto, "You've never used your quirks together, have you?"

Shouto shakes his head with a frown. His father forces him to use his fire side when they're training together, but his tutors all focus on his ice quirk.

"Shouto-san doesn't have an 'ice quirk'," Izuku gestures one hand, "or a 'fire quirk'," then the other. "Shouto-san has a 'fire and ice quirk'."

"I'm…not sure I follow," the tutor says nervously.

"Ice quirks can't make things out of ice. They can only freeze things. But just now, Shouto-san created ice and aimed it, didn't he?" Izuku walks back to the steadily shrinking flames and takes a deep breath. "…Ice quirks are based on the laws of thermodynamics. But fire quirks aren't. Or at least, not properly? Ice quirk users have high body temperatures, and are more energetic. They can even live off four hours of sleep. But fire quirk users have normal temperature relationships. Shouto-san, you can feel hot and cold, right?"

"R…Right."

"I was thinking of how Shouto-san's quirk might work for a while now, but I'm happy I get to see it myself." Izuku's fingers are perched on his chin in a thinking pose. "Now that I think about it, perfect quirks are kind of similar in that way…Clean combinations are unexpectedly powerful, aren't they…"

Shouto scowls.

Izuku looks up. "Shouto-san, freezing things and creating ice are different to you, right?"

"Huh?" Shouto blinks. "How did you know that?"

"Because creating ice violates the laws of thermodynamics, but freezing things doesn't. Even though the air was damp the first time we met, it wasn't like there were humidifiers all over the room. Even though the ice was brittle, you shouldn't have had enough to ice me over." Izuku strolls through the fire and picks up Shouto's water bottle.

"What are you…"

"Most fire quirks — including Endeavor — use the release of gas. That means your body is designed to be able to store a certain chemical and release it when needed." Izuku closes in on Shouto and presents the water bottle. "You drink a lot of fluids, don't you?"

The way Izuku keeps finding things he has no way of knowing is starting to unsettle Shouto a little. "Y…yeah."

"It's like I said. It's not a 'fire' quirk, and it's not an 'ice' quirk. It's a 'fire and ice' quirk." Izuku throws his arms out wide. "Because you can control fire, your body is designed to release gases. But because you can create ice—"

"Water vapor," the tutor says suddenly. "Shouto-kun creates ice by releasing water vapor, but—"

"But his quirk isn't perfectly broken up into two halves, so a lot of the flammable chemicals end up mixed in," Izuku finishes, sounding bored. He pinches Shouto's wrist hard enough to make him flinch. "I wanted to know about his body, though. Shouto-san's quirk is so amazing, I got it all wrong!"

Shouto stares at the pinched hand. He doesn't have an ice quirk. Even his right side can't escape his father's influence. He had decided that he could be a hero with only his ice, and then, just like that, some outsider crushed his beliefs so casually.

Shouto is overtaken by a sudden and visceral urge to punch Izuku hard enough to break his nose.

"What did you believe Shouto-kun's quirk to be?" The tutor asks, ignoring Shouto's problems, as usual.

"Like I said, freezing doesn't violate the laws of thermodynamics. People who use ice — or, freezing, really — quirks run really hot, like I do, because they're absorbing energy from the atmosphere around them. Heater quirks are the opposite, and constantly run cold, because they're taking energy from their bodies and putting it in the atmosphere. But since Shouto-san has two quirks, I thought that he must be absorbing energy and expelling it through his fire." Izuku pauses, and runs a finger along Shouto's arm. "Hm…Well, actually, it might still work that way. If the fire side affects the ice side, then the ice side should affect the fire side. Shouto-san's quirk is probably stronger than Endeavor's."

"Yes," Shouto murmurs, "that was the idea."

"…I'm kind of disappointed though…" Izuku's finger trails up to the bandage over Shouto's eyes, and then past it, to the centre of his hairline where his two halves split. "I was hoping that since Shouto-san's quirk was exothermic and endothermic, we'd have something in common. But he's more amazing than I am."

"That's just how I was designed. Of course a child who was born normally wouldn't compare," Shouto grinds out.

Izuku quirks his head. His eyes are tracking, but Shouto can't pick out what part of him he's looking at. He seems frustrated, all of a sudden. "…That's not true. People can have perfect quirks completely on accident. But it's still their quirk. Even if people tell you that you're perfect, or that you can do no wrong, or that you're destined to be a hero, it's your quirk, and if you use it wrong, that's _your_ fault."

"Did my father tell you to say all that?" Shouto asks hotly, "did he teach you all that thermodynamics stuff? Is that why your mom came? Just to make me use my quirks together? _I said I didn_ _'t want to!_ "

"He didn't! I spent months learning these things! I filled up my notebooks to the brim!" Izuku grasps Shouto's other wrist with a furious look on his face. "I did it because if I let myself think that my quirk is useless, then that's my fault! If I stop short of being a hero because I couldn't think of a way to make it heroic, then I've used my quirk wrong! And that'll be _my_ fault!"

"Izuku-kun, please-" The tutor starts.

"Why do you want to be a hero?" Shouto asks impulsively, drawn in by the intensity.

"'Cause I want to be like All Might! Even if I can only be a sidekick, I want to be a symbol of peace too! I want to be so dependable people feel like there's nothing left to fear!" Izuku says. The truth of it gleams in his eyes.

"All Might…" Shouto had also… "He's amazing."

"Right? Did you see his debut? They had only had licensed heroes for about a decade, and he saved a whole plane! Everyone should have died, but he rescued all of them! He came out of nowhere, and everyone just sort of knew, you know? I think that's the biggest part of being a hero! You arrive on the scene, and they all just _know_!" Izuku clenches Shouto's hand in his. His smile lights up the shadows that were hanging over his face before. "If I can't make people that confident that I've saved them just because I'm there, I've failed as a hero! Right?"

When it's stripped of its prestige and its success, Shouto can see the appeal of heroism as he used to. When he watched All Might on TV, he admired him enough to want to be a hero too, but he hadn't thought hard about why that was. He doesn't think it's the same reason Izuku does, but…

"Not like Endeavor…?"

"Hm? Oh, I guess Endeavor is really strong. But I don't think he's all that useful unless he can go all out…" Izuku muses.

Shouto sputters with surprised laughter.

"Ah," Izuku says in surprise.

"Do you think my quirk is really stronger than Endeavor's?" Shouto pushes.

"Mmm…Well, once you're all grown up, it should be."

"But is it more useful?"

"I think so. It's harder to seriously hurt people with ice."

"Okay." Shouto shakes his hands free. "If it's my quirk, I'll use it properly."

"Splendid, Shouto-kun! I'm sure you'll be a wonderful hero, like…" The tutor drops his voice a little. "Like All Might."

"Oh. So, since you're using it together…" Izuku takes a few steps back. "Let's practice making explosions again! I'm pretty good at dealing with those already!"

Shouto lets his breath out. Izuku is unreal. He had the willpower to stare down not only Shouto, but Endeavor himself, to show off his quirk — which Shouto thinks isn't all that impressive — and say _I_ _'ll use this to be a hero_ without a lick of self-consciousness. He has the unshakable determination Shouto was pretending he had. Using his natural genius to understand the world around him and how to play it to his advantage. The self-control and discipline he has shines in comparison to Shouto's meek complaints. Shouto can imagine feeling safe in a crisis simply because Izuku was there. It's pathetic that he can't think the same about himself.

Shouto doesn't want to live up to his father's expectations, but he thinks he can settle for Izuku's, at least.

* * *

Shouto-san is really nice!

Izuku doesn't usually talk to people who aren't Kacchan and his friends, especially not people his age, so he's excited sparring cram school is working so great with Shouto-san and his tutor. Izuku has forgotten the tutor's name, but Shouto-san doesn't seem to know either, so it probably doesn't matter!

Izuku thinks Shouto-san wasn't sure what kind of person he was, so he didn't want to talk, but now Izuku is clear as clear can be, and Shouto-san gets it! Izuku knew he would. Everyone loves talking about All Might. See, friendship is easy. You don't have to be Kacchan to get excited about All Might. In fact, it may actually be more desirable to not be Kacchan! Ever!

Especially not right now.

"I said to shut up about thermos-whatsit! If I don't get it, I don't get it! Why do I need to know this stuff, my quirk is already awesome!" Kacchan hollers, kicking at Izuku's hand so he'll stop writing. Izuku thought that since they're alone today, Izuku would have enough of Kacchan's attention to explain some of the basics of science to him, but apparently not.

"You say that, but I managed to figure out how to make your endurance better, didn't I?" Izuku huffs.

"Then you do all the thinking! You're the sidekick, aren't you?" Kacchan scowls.

"…If you fail the practical exam, you can't get into U.A., you know."

"I'm doing just fine in school, you're just a freak who studies too much!"

Izuku looks back at his notes. "Fine. I'll just tell you my ideas. But you better listen to them."

"I think heroes and sidekicks listening to each other is part of heroism. That's why I get to boss you around," Kacchan says.

Izuku wants to complain, but rather than pushing it, he takes his kit out of his metal lunchbox. "Since you explode things, you're going to cause a lot of shrapnel. I want to see how your body deals with puncture wounds so you know if you should make it part of your costume."

"Is it going to hurt?"

"Probably not more than getting punched?" Izuku takes out his geometry compass. It's the only blunt point he owns that can safely be forced into the human body. "Stand up, I'm going to put it in the side of your butt."

"What? _Why?_ "

"Because there's a bunch of fat in the butt, and it absorbs shock. I want to do it in the side of your butt so you can still sit down properly."

"So it'll hurt less?"

"Yeah. Lots of people recover from bullet wounds to the butt." At least Izuku is pretty sure they do. "It's like the opposite of a kneecap."

"Oh, yeah, that makes sense," says Kacchan, who is already intimately familiar with the concept of 'kneecapping', and also falling down and banging his knees.

"Hold still." Izuku holds him by his hip with one hand to steady both Kacchan and his aim, and gives Kacchan's side a quick jab, careful to avoid any bones. Kacchan lets out a short scream of pain. "Now check for broken skin?"

Kacchan reaches down his pants and rubs it. "Doesn't feel like it…" He pulls his fingers out. "No blood."

"That rules out most shrapnel. I can't test small high-speed pieces without seriously hurting you," which is bad, according to Izuku's mom, "and I'll need a blunted scalpel to check how you deal with edges."

"I'll be throwing shrapnel at you too, though. My turn." Kacchan makes grabby hands at the compass.

"Oh. Good point." Izuku stands up and pulls his pants forward because he doesn't trust Kacchan to guess where the side of his butt is. Kacchan takes the compass and aims carefully.

Izuku's knees buckle when the compass is driven in, and tears spill over. Kacchan has way more endurance than he does. He checks to feel — the compass left a deep imprint, but it didn't break skin on him either. Hmmm. That's useful.

Izuku records Kacchan's durability in one notebook, and his own in another. Most people have shock-absorbing skin, though, so it's not a huge deal that they both have it. Izuku is pleased they're still compatible, though; he's building his base as a viable sidekick! Sooner or later, the populace won't think of one without thinking of the other! And also people won't worry about Kacchan being too noisy and villainous because once they go to U.A. Izuku will teach him manners. Not right now, though. The reason both of them can train so often together right now is because no one expects them to have manners. People with manners probably don't stab each other in the butt with compasses.

"Is this whole book about me?" Kacchan asks suddenly.

Izuku flinches when Kacchan picks up his book. It's already half-full and caked in white-out from each time he made an assumption and had it proven wrong, which has happened…more than Izuku would like. Kacchan looks happy with it, though, so Izuku pulls back, though his hands still hover uncertainly.

"It's, uhm…for our hero progress…Mine has a bunch of notes about you too…" Izuku murmurs. His face burns.

"Of course it does. Your quirk is useless on its own," Kacchan laughs.

Izuku shrinks. "It's…It's not useless. I can take even Endeavor's fire."

"But you can't use it to fight, can you?"

"I can use it to rescue! Do you know how many fires are started during hero battles?" Izuku grasps his trouser legs. "Just because I make you stronger…doesn't mean I can't also be strong."

"Well, I'll look cooler next to you. Oohh, is this all my hero uniform ideas?" Kacchan leans in close, ignoring Izuku's wobbling lip. "Oh, so this one is if I can't take shrapnel, right? This other one looks uncool, though. Wanna see my drawings?"

"It's fine." Izuku weakly takes the notebook and pulls it back into the pile so he can stuff everything back in his bag. "I'd rather see Kacchan fly."

"Oh, right!" Kacchan jumps to his feet. "I increased my range! Watch!"

Izuku studies the balance. When Kacchan lands, he adjusts the direction Kacchan is holding his right hand, and warms his palms so he can blast off right away. It's no different from usual.

When he gets worn out, Izuku clutches his bag to his chest. "Uhm, Kacchan…"

"Ah?" Kacchan opens one eye. He's breathing to heavily to say it with much energy.

"My birthday is next week…"

"And?"

"I was wondering if you wanted to come to my house?" Izuku asks hopefully.

"I dunno. Maybe." Kacchan closes his eyes again and sighs. "Damn…Hero training is so hard…It's good I got you. Everyone else just wants to mess around."

He wasn't feeling confident, but that one comment gives Izuku enough energy to smile.

"Yeah! That's what sidekicks are for, after all!"


	7. Preperation Leads to Results

**Experiment Seven: Preparation Leads to Results**

* * *

Shouto's idea of heroes has always been a simple split between 'heroes who are good and heroes who are bad', or 'heroes like Endeavor and heroes who aren't', and he's he's never thought beyond that. He didn't think he'd ever need to, and actually having someone describe their motivations and ideals has shaken him a bit. He never thought heroes had important personal motivations. He thought heroes just sort of…happened, maybe, or when you overcame things, you became a hero. Heroism is a dream you have and then achieve, not a process. Something like that.

Sure Shouto respected All Might, and felt safe with his halo of influence standing over him, but he never thought it was an ambition All Might set out to do. As for Izuku, well— well, Izuku is determined enough that Shouto trusts him, a bit like All Might, but learning Izuku _actively wants to give off that effect_ , that's new territory for Shouto. In fact, Shouto thinks that may actually be twice as cool as a 'not like Endeavor' hero, which makes him twice as cool as every hero Shouto has cared to think about in the past few months, which makes him one of the coolest people Shouto has ever met.

But anyway. Hard work.

Izuku phrased heroism like a thing you have to work your best at. If you're a cool hero, like Izuku is probably going to be, you've got to have cool ambitions, like making people trust you. And people won't trust you if you hold back your abilities for some petty personal reason that doesn't really matter. If he just keeps reminding himself of that, he won't have to keep starting fights with his father. He'll sneakily be the perfect hero, and it will have nothing to do with Endeavor.

The next matter is the attitude. Projecting the feeling that you have altruistic ambitions. All Might is really popular because he's so good at it, and Izuku has that part down a lot better than Shouto does. Hmmm.

After P.E., one of the students in class picks up all the balls for everyone, even though he was on the winning team. Shouto stands in place for a moment, and then realizes the natural generosity for what it is. _Heroic attitude._ It's altruistic to help even if you're not obliged to.

He approaches his classmate and places a hand on his shoulder like All Might does on TV. "You can be a hero."

"H-Huh?" The classmate jerks back in surprise.

"You're a good person," Shouto clarifies.

The classmate flushes and laughs a little. "Th…thanks, Todoroki…"

Shouto nods resolutely. Positive reinforcement is a good hero thing. His dad would have scoffed at such menial tasks. Because he's the wrong kind of hero. But Shouto is going to be the _right_ type of hero. It's very important people know this.

"I'm going to be a hero," Shouto adds out loud, "and I think doing nice things for people is important."

"Me…Me too?"

Shouto smiles and wanders back to the rest of his class.

What else makes a good hero? Well, determination and confidence, but he doesn't like those. _Definitely_ not a 'perfect quirk'. There's no way Shouto would be a hero with just his quirk, he'd hate it. If he's going to use his quirk, he needs to find out the perfect way to make it useful, with _ingenuity_ , just like Izuku does with his own; Izuku _seems_ useless, but he got it this far because he thinks like heroes think. Anyone can be a hero. All Might said so on TV. Brute force won't cut it. It's sort of like how All Might's quirk is punching really hard, but he can basically fly as well. Because he _thinks. Heroically._

A girl drops her books. Shouto leaps to help pick them up. He claps her on the shoulder too, since it seems like a good habit to build, but he can't think of what to say, so he just nods at her and drops it. He's doing fine anyway.

He goes to the nurse's office to have his burn examined during break. It's been a few months, and they should be moving onto an eyepatch soon. Scars get less severe with age, but the one on his face is fresh, and really ugly to look at. His dad wouldn't let him get skin grafts, so it's going to end up a pink smear over his face forever, even after it finally heals. They're going to fix his eyelid later. He could have recovered right away, but his father was worried about the press; he said he didn't want people looking into Shouto's mother. He said she's better off figuring herself out without people pressuring her. He said a lot of things.

In class, he tries to pay extra attention. His grades are already decent, but he wants to go above and beyond, because he remembers sometimes students study together and help each other out, which is _heroic thinking_. Shouto is also worried that Izuku will leave him in the dust with all his complex science terminology. He's Shouto's age, but managed to figure out all that quirk stuff in seconds, just by tasting his ice. Shouto doesn't think being smart is heroic, per se, but it was still really cool, so he wants to understand anyway.

He gets driven home, as always. Shouto looks up through his fringe at his father, waiting for him in the main entrance hall, with his tutor.

"I heard you're finally willing to train both sides?"

Shouto shoots an accusatory look at his tutor, but doesn't answer.

"Good, Shouto…you're finally seeing what you have to do!" His father places a big, calloused hand on Shouto's head and ruffles his hair. The gesture of affection is strange, coming from him. It doesn't feel right. Shouto shifts uncomfortably.

"We'll be training a bit today, as well," the tutor adds eagerly.

"I'll supervise, then. I can spare an hour or two to see what Shouto's achieved so far."

Shouto grimaces. They've spent all these sessions catching Izuku up, without any quirks; yesterday was the first time Izuku was allowed to spar normally. He's worried his father will see Izuku fumble and misunderstand. Shouto's not used to thinking like a hero, he wants Izuku around more often so he can make sure he's not doing it wrong. It's not like he can call up All Might for 1-on-1 advice.

They wait in the hall, with the tutor working Shouto through his hand-to-hand combat, no quirks. His father can't complain about that; he already knows the humidifiers need time to dampen the air. While they strike at each other, Shouto keeps nervously casting his eyes towards the door. If Izuku screws up… _Could_ Shouto find a heroic-minded person to help instead? He doesn't think so, not with his father breathing down his neck. What about his siblings? Are his siblings heroic-minded? He can't remember what they're like. He's barely ever spoken to them.

There's a knock at the door. Shouto pulls his hand out of a strike he was aiming at the tutor's chest and gives his father a baleful look.

"Come on. I'd like to hear the boy's interpretation of your little change of heart."

The grimace deepens.

The tutor goes to the door and answers it.

There, standing with his feet in the air, is Izuku.

He's wearing thick work gloves and his training robes, held in a wobbly balance that doesn't look like it'll hold. Izuku carefully walks with splayed palms all the way to the centre of the training hall. Endeavor is staring. The tutor is staring. Shouto might be staring as well.

"Okay," Izuku huffs. He bounces his elbows a few times, nods, and with a sudden burst of warm air, flips upright. He doesn't manage to get his centre of gravity far enough, and has to shuffle backwards to accommodate. He still looks satisfied, and glances towards Shouto with a grin.

Then he notices Shouto's father. "…Sir."

"What was that?" Endeavor asks with a slow, deliberate tone of voice that makes Shouto's stomach churn. He's not allowed to hit Izuku, right?

"I was practicing balancing, sir," Izuku says quickly. "I don't want to be disoriented if I lose my balance and fall back, or if I injure my legs and need to walk on my hands, or if I have to do a backflip and—"

"The flip," Endeavor interrupts.

"Oh. That was my quirk."

"Your…temperature moderation quirk?"

"Yeah." Izuku raises his hands and releases a burst of warm air that ruffles Shouto's hair. "I can release warm air sometimes. Especially if I hold my breath."

"Enough to propel you?"

"I was hoping I could, but it looks like I can't. Hopefully I can in the future. I ran an experiment with my mom where the amount of pressure I release, the temperature, and the length I can release it was recorded, and I figured it out." He holds his breath, touches the back of his neck, and then releases the air again. This time, it's a blast of hot air. "The higher the temperature, the more the warm air expands, the more it uh…hot air rises, right? Like…like in movies with the pressure stuff that expands so fast all the screws and bolts and things will pop out. Because the air is expanding. I can do that inside my body."

Endeavor folds his arms. "And where are you getting this temperature…?"

Izuku turns around and loosens his robe to reveal a small dot of glowing orange skin, surrounded by a ring of warm red. "I have to keep it small, or else it'll expand too fast like the blowtorch experiment did."

Shouto's mouth parts. Did he just… _fabricate a second quirk by manipulating the rules of his first one_?

Endeavor looks stunned too, but after a second, he bursts into laughter and reaches out. Shouto twitches, but all Endeavor does is place a hand on Izuku's head. "Not bad…A worthy mind, as well as a useful body."

"Thank you, sir," Izuku says quietly.

"Shouto!" Endeavor shouts, and Shouto flinches again. "I want you to think of five new techniques with your quirk that don't involve covering something with ice or fire by the end of the month."

"But I only just started to—"

"You've been training each individually for years, _Shouto_ ," Endeavor booms, loud and deep, "If you have this boy to assist you, surely you'll think of something. You're not going to match All Might by simply having a quirk."

Shouto's eyes water and he opens his mouth to argue, but when he meets Endeavor's glare, he shrivels and bows his head. "…Yes."

"I'll leave you to it. I want to see the results all at once." Endeavor removes his hand from Izuku's head and marches out the door, slamming it behind him.

Shouto's lip trembles, and he bites down on it. He doesn't have the will to look at Izuku.

Izuku makes a small humming noise. "I can probably get all five right away. The first one's definitely explosions."

"Why'd you have to do that?" Shouto asks quietly.

"Huh?"

"Why'd you have to show off in front of him?"

Izuku blinks slowly. "…He asked me how I did it. I had to answer him."

"Why'd you have to come in so weird in the first place?" Shouto's voice rises to a half-shout.

"I didn't think anyone else would be here." Izuku stares at him for a second, before frowning. "I'm sorry."

Shouto clenches his teeth and looks away.

"So, explosions…" Izuku taps his chin with the crook of his finger. "But Shouto-san's reactions don't feel like Kacchan's at all…The flexibility depends on tiny stuff like that…"

"So you can't think of anything?" Shouto asks nervously.

The tutor steps in. "Well, we have a month, so we can—"

"Shouto-san," Izuku interrupts. "Can you coat your hands in ice using the reflex you use for your fire, and then set them on fire?"

"They'll explode," Shouto argues.

"Wear earplugs," Izuku suggests.

At a loss, Shouto coats his hands in several layers of ice, and sticks them as far away from his body as possible. He gives Izuku a nervous look. Izuku smiles at Shouto's hands, waiting patiently for results, so Shouto has no choice but to go ahead and do it.

With a twitch starting at his shoulders, his flames slide down his arms in a smooth arc that ruffles his sleeves before ballooning into a searing explosion of flame with a core so white it makes Shouto's damp eyes brim with new tears. A streak of blue fire blooms back up towards his face. He flinches away, and the muscles in his injured eye twitch rapidly.

They die down to a steady flourish. Izuku takes a finger in his hands and smells it, then fidgets with the other digits for a minute, until finally the Flames dissipate.

"It's not detonating," Izuku mumbles, "at least, not in the traditional way. It's more like a fireball from gasoline. The explosive element might have been because the air in the ice was expanding — Shouto's ice structures are usually hollow. Expanding gases make metal boilers and stuff creak and pop bolts and explode."

"How scientific," the tutor mutters under his breath.

"Very. I don't know enough to write them in papers though." Izuku pops one of Shouto's fingers in his mouth, making Shouto wrinkle his nose. Izuku lets it sit there even after licking it, biting down every now and then, before releasing it. "It tastes stronger when you're doing it intentionally, huh."

"…Obviously," Shouto says.

"Hm. Then, fireball is the first move." Izuku darts to the far wall and outstretches his arms. "Shouto-san, can you make a line of ice using your fire reflex to me?"

Shouto obeys, understanding roughly what move Izuku wants to make. Fire blooms up in a wall between the two. "…Guided fire."

"That's two. Number three is something you'll probably want to train to do, it sort of feels hard even though I don't have a quirk like yours. We'll do that next time I come over. Number four…Do we have anything flammable?"

The tutor takes a magazine from the side bench and hands it over. Izuku points it towards Shouto, hesitates, and then just sticks it to the back of his neck. After a second, flames start snaking up the paper. Izuku places it at the ground. "Shouto-san, can you shoot pieces of ice?"

"U-Uhm…no. I can throw them normally though."

Izuku quirks his head, taps his chin with the crook of his finger, and nods. "Okay. That's fine."

Shouto grows scales of ice along the surface of his arm, mood picking up now. He needs to toss a few times before he manages to hit the flaming magazine. It explodes.

"Number four," says Izuku. "Number five…well, it doesn't have to be for combat, right?"

"He…didn't specify, no," the tutor says slowly.

"Okay, good. Number five — Shouto-san I think it might be hard to switch between Flame reflex and uhhh, your ice quirk how it works with your mom and sister so can you only use ice from the atmosphere?"

"Of course," Shouto says defensively, "you didn't explode when I had to cool you off during your introduction, remember?"

"Oh! Yeah, I forgot. Okay, uhhmmm…Sensei, do you have a pen?" Izuku asks.

The tutor has to get one from the changing room. Izuku bounces on his heels, looking pleased. Shouto shifts from foot to foot, feeling excited too.

"How many ideas for my moves do you have?" Shouto asks.

Izuku quirks his head. "About 12 before I realized your Flame-based ice doesn't detonate. Maybe 8?"

"Just now?"

"Oh! No, I spent all night planning them out. Your quirk is really interesting, and you sounded like you didn't want to use it like one or the other. I thought it was a shame if you became a hero feeling bad about your quirk."

"Oh, no, I…" Shouto fidgets with the hair at the nape of his neck. "I changed my mind back then. I-I don't mind. Being a hero with my quirk, I mean."

"Oh, I didn't realize!" Izuku looks happy. "That's good! Well, I'll add individual skills to my research later, too, so you'll be extra prepared to save people."

Shouto clenches both his fist and his jaw and nods. _Heroic thinking!_

The tutor returns with a pen. Izuku holds it out. "Okay, I didn't really think hard about this one, but we need a whole lot of time to practice. So create an egg of your Flame-reflex ice around the end of the pen. Make sure it's thin."

With some effort and a lot of hand-waving, Shouto manages a decently round circle around the tip of the pen. He looks to Izuku for the next step — he genuinely doesn't understand what he's getting at, here.

"Now, coat the egg with ice from the atmosphere. Make it thicker."

It's a lot easier than doing it by reflex, though his hands instantly go numb with cold. He clenches them to get them circulating again as Izuku inspects his work.

"…Right, let's see…" Izuku plucks the double-layered orb from the pen. "Okay, it's working! So now you just set it on fire and cap it."

Shouto gets it now, but he's not sure why it could be considered a special move. He lets a blossom of fire loose inside the egg, and then quickly caps it with ice as a massive tongue of flame lances out. He's left with a glowing orb.

"Lamp," Izuku explains.

"…Oh. For rescue," the tutor realizes.

"Yeah! Shouto-san doesn't really need flashlights with his quirk, so this way it's kinda like sharing."

 _Heroic thinking!_

"This one's my favourite move," Shouto says immediately, so Izuku knows he's a heroic thinker.

"Okay. We'll train this one a lot too, then," Izuku beams. "So you like my ideas? Really?"

"You're so smart. You're like a genius."

Izuku turns a little pink and rubs the back of his head shyly. Shouto narrows his eyes. He almost forgot. With a hand covered in atmospheric ice, he touches the back of Izuku's neck. "Don't let that keep going."

"Oh! Sorry, I forgot I left it like that." Izuku bows his head so Shouto can access the spot of red-hot skin easier. "Thank you, Shouto-san!"

"…No problem." Shouto can feel the warmth prickle painfully against his skin, but it can't pierce the layers of ice he put up. Eventually, when he can't feel any warmth from Izuku anymore, he pulls away.

Izuku whirls on him. "Hey! Shouto-san! do you want to come to my birthday party?"

* * *

 **Shouto** : Izuku is so cool…so heroic…

 **Shouto** : [very deliberately does not think of how Izuku managed to superheat a portion of his skin just to create a very small amount of warm air or what would lead him to that conclusion to begin with]


	8. Have a Strong Heart

**AN:** The raw copy of this was a train wreck, thank you SO much SimK for saving my life as my beta

* * *

 **Experiment Eight: Have a Strong Heart**

* * *

Izuku's father is out of the country, but that doesn't mean Izuku's father is out of his life.

…More or less.

"I have no idea how to get back home," his dad sighs through the tinny speaker. "I'm sorry, Izuku, I know this is important to you, but—"

"Can you call on the video?" Izuku interrupts, clutching his mom's phone tightly to his ear.

"Probably not. My connection is…"

He's right, of course. The call is fizzing and popping, even on a landline. Izuku kicks his legs back and forth. "Can you call me for my whole birthday?"

"I think I may be able to do that, at least."

"Okay, good. Make sure you get a cake in where you are so you can eat cake with us!" Izuku bounces on his seat. "We're eating black forest cake so that's the cake you have to buy."

"I'll do that. Have you got my present?"

Izuku leans over eagerly. "We got it! It doesn't make any noise when I shake it and it's not very heavy. What is it? Is it made of fabrics?"

"You'll just have to wait and see, won't you? How's school?"

Izuku's mood sours a little. "…Okay. Me and Kacchan are figuring out hero costumes and uhmmmmmm I think I made a friend because he said he's coming to my birthday. He's really nice and likes All Might a lot and lets me play with his quirk. If you have any toys and stuff like what I got on my sixth birthday I would like that as well, please."

"…I'll be sure to keep that in mind. It's nice you're making more friends your age."

"Yeah. I hate Kacchan's friends. They're boring and they don't understand us. I think they're jealous because they know I'm gonna be Kacchan's sidekick and they won't be. 'Cause they suck. Shouto-san's way better and nicer also, and, and—" Izuku tilts his head, trying to remember if he was going to add anything there or not, "—and he'll be a cool hero, I think. I wish he went to my school instead of a different one."

His dad laughs, low and soft and warm. "Yeah?"

"Yeah. Are you making any friends at your work?"

"I think so! I've been a little swamped training all the new employees, though, so I can't spend time with them. The turnover rate is…well, it's good I'm in management right now."

"Oh. What's a turnover rate?"

"When too many new employees quit very, very quickly."

"Oh." Izuku stares at the linoleum, face scrunched up. "So because you're managing you have to train every single replacement over and over again. And that means you can't take breaks."

"That's right."

"Ohhhh. I hope it'll stop turning over soon."

"I hope so too. Can you pass the phone to your mother?"

"'Kay. I love you!"

"I love you too."

Izuku passes the phone to his mom, who takes it with a smile. Izuku hops down from his chair and wanders back into his bedroom while she talks to his dad in the kitchen.

This isn't going to be his best birthday ever, but it's going to pretty good, and that's what _really_ matters.

* * *

Shouto has never celebrated a person's birthday before.

Maybe his own? His mother would give him a small little celebration with just the two of them. So maybe he sort of knows. There's…a cake, and gifts, and…and he's allowed to do more things than usual. There's never any training on his birthday. They're special days.

This year will be his first birthday without his mom, so he doesn't know what birthdays are like now. He hopes they still have no training. It's okay if there's no cake.

Shouto's fingers twitch in his lap.

So…well, he ought to give Izuku a gift. That's how it's meant to happen. Gift-giving. Of course.

He doesn't think his father will let him buy a present for Izuku. He's not sure his father would buy a present on Shouto's behalf, either. It might be hard to even get to the party. Endeavor's legacy is his best-kept secret, and Shouto is usually forbidden from spending time with other children his age, and even if Izuku is privy to the goings-on of the Todoroki household, even if his father _likes_ Izuku…Shouto doubts he's going to be able to show up, gift in hand, unless he's sneaky about it.

Shouto has to go straight home after school, and he hates being followed around by attendants, so he hasn't gotten the opportunity to buy things with his allowance. When he pulls it out of his drawer, it looks like a lot of money. He's never counted it.

This is… _present_ money.

Now, to get his present money out of the building, and exchange it for presents.

His tutor must have informed his father about Izuku's birthday by now. If he's seen, they'll know what he's up to. He has to proceed with the utmost caution. Many heroes use stealth to their advantage. This can be considered training.

Shouto opens his window and peeks through it. His bedroom is on the second floor, and outside the hallway around his room is a balcony that overlooks the inner yard. If he goes down the stairs or down over the side of the balcony, he'll definitely be seen by…somebody. However, the bedroom window is a straight drop. Well, there's a ring of wood supports, but Shouto doesn't think that counts. It's not like he can drop straight down.

He narrows his eyes.

How would _Izuku_ escape?

Well, there's…hm. He definitely can't use his fire quirk. He could freeze himself to the building, but he doesn't think he could take steps down that way. He doesn't have the precision to make handles, either.

…But he does have the precision to make orbs, doesn't he? It's not like he can't make shapes at all. He can make pillars that are tall, and pillars that are thin, and pillars that are fat. He can…

"Oh!" Shouto takes a bottle of water from his desk and uncaps it. He climbs up onto the windowsill and sits there, hand gripped on the sides carefully, and gently lowers the water bottle until it begins spilling over the side of the building. Once it's emptied, he takes a deep breath, lowers his hand, and feels a sinking bloom of cold seep from his body. He presses it against the wall underneath him, and gives it a slap.

A flat blade of ice shoots from the surface.

Shouto smiles and gently slides down to stand on it. It's hollow, as usual, but firm enough at the base that it shouldn't break as long as he doesn't give it a good smack, or something. He leans over and presses his hand to the wall again to make another one.

Shouto gradually produces a staircase made of ice. It gets weaker and weaker the lower he gets, until he's forced to depend on the liquid in his body to keep the steps solid. It's still working, though. He's doing it! He's making the best of his quirk!

He steps down to the next ice platform and his stomach bottoms out when, with a high, tinkling _**CR-CR-CRACK**_ , the step shatters under his feet, sending him sprawling to the ground.

The shards of ice are so weak that they collapse when he lands on them. Shouto tries to take a breath, and grunts when he can't. It comes in a few short gasps before he catches his wind again.

The window directly above him whips open, revealing his sister.

" _Shouto_?" She balks.

Shouto looks up at her with a wide, horrified eye. His ribcage aches too much to risk wasting his air to say anything.

"What are you— oh." Her gaze travels up to the wall right above her head, where Shouto had made his ice staircase. "Is that your room up there?"

Shouto swallows and rolls over. He feels like all his organs got a good and thorough jostling, but stretching a bit makes him feel a little better. He rolls his shoulders and tries to take a few deep breaths. It's really hard, but after a few coughs he thinks he can breath normally, if not deeply.

He peeks over his shoulder to look at Fuyumi, who is frowning at him.

Shouto tries to crawl away.

"Shouto—" She hops out of her window and catches up to him before he can get to his feet. "Shouto, stop. I'm not going to tell Dad."

Shouto pauses. He shifts to look at her suspiciously.

She gives him an earnest smile. "Promise."

Shouto turns to look down at the ground. He pulls out his wallet and clutches it to his chest. He's never really spoken to Fuyumi. Or he has, but it's never been a conversation? He doesn't know her. Their schedules are different, their ages are different, their expectations are…

His lower lip trembles.

"What do you got there?"

Shouto flinches back and stumbles to his feet. "It's nothing, I—"

Fuyumi is still smiling patiently at him. If she notices the tears welling in his visible eye, she doesn't show it. No longer how long the silence stretches, she doesn't demand for him to answer. She just looks expectantly, without judgement.

Shouto bites down on his trembling lip and parts his hands so she can see.

"A wallet?" She leans in closer. "You trying to go buy something?"

He nods.

"What are you getting?"

"P…Present," he mumbles.

"A present?" She lights up, moving out of his personal bubble to clap her hands together. "Who for?"

Shouto straightens his posture a little, but winces back into a hunch when his ribs twinge. "…I…Izuku."

"The temperature kid?"

Shouto nods.

"Do you know what you're going to get him?"

Shouto's face falls, and he shakes his head.

"Okay. Let me go grab my shoes."

His head whips up to look at her. "Huh?"

Fuyumi bounces backwards, still beaming at him. "I'll help you pick something out, okay? I can't let a kid like you run around unattended! Wait here for me!"

She bounds back into her bedroom window, leaving Shouto alone in the bushes around their house. A weaker pillar falls from the wall and drops to the grass with a hollow _thunk_. He hears her door opening, and then footsteps leading away. He follows the direction they went, even when he can't hear them, to the front of the house. After a second, he can hear a small little thump, a click, and Fuyumi bounds out of the house.

She whirls to look to the side of the house, where Shouto is standing meekly.

"Let's go!"

* * *

Fuyumi didn't expect her first meeting with her youngest sibling to be in an act of open rebellion.

There's not a lot of staff besides the tutor, the two cleaning ladies that are only around during afternoons, the chef, and the matron. Fuyumi isn't sure if Shouto would even know that, considering she's only ever seen him on the second floor and in the dojo. It's easy to escape out the gate unseen, though Shouto looks like he's going to tremble out of his skin.

When they hit the open streets he finally manages to unwind, actually looking around at the stores lining the road. At first it's with guarded caution, but the longer they walk, the more openly curious he is. By the time they reach the trains, he's begun zig-zagging on the sidewalk and bouncing a little as he inspects the shop windows.

"You think that's impressive, wait until we get to the mall," Fuyumi laughs.

Shouto's not like her other brothers, that's for sure. Fuyumi's siblings are raw compressed energy, for better or worst, boisterous and uncomfortably intense. It's only the stretching patience of her sisterly obligation and a united hatred of their circumstances that keeps them together.

Shouto, though, is quiet, and meek, and keeps looking at her like she's a threat instead of a guardian. Ever so often, he'll remember that she's standing behind him, and his excitement will flag, but then he'll get distracted by something new and get wrapped up in it again. It's like he's seeing the world for the first time.

 _Is_ he seeing the world for the first time?

Suddenly nervous now, Fuyumi outstretches her hand. "S-Shouto! Hold my hand while we're on the train, okay?"

Shouto stares at her hand for what feels like forever before he finally takes it in his own. Fuyumi tugs him lightly into Musutafu station, careful to avoid any crowds. She doesn't know how notorious Shouto is; he goes to school as a Todoroki, doesn't he? But if he's allowed to go to school, does that mean he's not usually bothered? Urgh, she wishes she could have gotten to know this kid before taking him out this far, but it's too late to stop now.

She buys tickets for both of them, and they wait for their train to come. Shouto leans over the edge, peering into the tunnel. "Where are we going?"

"Kiyashi Ward. It's the nearest Tokyo ward." And the one less likely to be overloaded with people on the way back. She's been stuffed in a Tokyo train car before, and it wasn't fun. "We're going to go to the mall!"

"The mall," Shouto repeats solemnly to himself.

"The mall has more specialty and hobby stores, so you're likely to find things your friend doesn't have yet," Fuyumi explains.

" _Friend_ ," Shouto repeats, twice as grimly, widening his eye slightly.

"Y…yeah. Do you know what sort of things Midoriya-kun likes?"

"He likes… _Heroes_ ," Shouto says resolutely.

"U-Uhm, yeah, I figured. Anything more specific…?"

"All Might! He likes All Might. He's going to be like All Might someday."

"Okay! I think it'll be easy to find some nice collectibles for him. Is it for his birthday?"

Shouto nods, and stops talking after that.

They board the train, and Shouto looks so panicked by the train as an entity that Fuyumi takes a seat and pulls him close next to her. He draws his knees up and hides behind them, clutching his wallet tightly next to his stomach, other hand still firmly grasping Fuyumi's. He looks hunted while the train is still in the station, but when it reaches the edge of Musutafu, he twists around to boggle at the passing scenery. His nose is pressed against the glass the entire trip, and he starts thumping on them on the glass when he sees Tokyo rapidly approach on the horizon.

His hand, his right hand, doesn't get clammy over time. It's a little cold, like his circulation is a bit low. Fuyumi's hand is the same, and the warmth between their palms is negligible, but still comfortable.

When the train arrives in Kiyashi ward, he's lost his caution and practically pulls Fuyumi out of the station himself. They reach the surface to skyscrapers that make Shouto stumble and swivel around, open-mouthed. A hero too high up to make out bounds from skyscraper to skyscraper on patrol, and Shouto watches with open wonderment.

"It's so big," he finally blurts.

"Sure is!" She laughs. He must not have ever seen a building over six storeys before. "It's like this in downtown Musutafu too, you know!"

"It _is_?" Shouto gasps.

"Sure! There's office buildings, and apartments…Oop, careful." She pulls him away from the road he was wandering towards in order to get a better look at the buildings. "You've never seen skyscrapers before?"

He shakes his head. "The buildings around school are short. And there's…tiny malls."

Strip malls, he means. So he _has_ seen them before?

"The Kiyashi ward mall is this way," Fuyumi says, pulling him back down the street. He stumbles to follow her, and clutches her side when they have to cross the road. The crowds are much thicker in Tokyo, and Shouto looks petrified by that fact.

Soon the familiar 'WOOKIEES' sign comes into view, bookended by palm trees, and the towering presence of the the mall itself behind it. Fuyumi is careful to watch for Shouto's height as she ascends; she's never had to walk with someone as short as he is. Well, not since _she_ was that short. He tries to keep up with her, though, so that's something.

When they enter, Shouto makes a startled noise at the central plaza, with its complex mosaic tiles and floors upon floors rising up above them, with walkways and stairs criss-crossing their way around the whole building. It's not a very big mall; the most impressive decoration is an _extra_ big palm tree amongst the dozen dotting the first floor. But for a kid who's never been inside a mall, it must be amazing.

Fuyumi walks him up to the second floor hero collectible store. He practically snaps his neck swiveling around to look at all the merchandise, and bumps into at least two people despite her best efforts. They finally trip their way to the back wall, entirely taken up by All Might merchandise, more than any other place in the store.

"Okay, so you should pick out something he'd like!" Fuyumi gestures to the shelves.

Shouto gazes wide-eyed at the toys, plates, coins, spoons, buttons, pins, and all sorts of other merchandise available to him. "Something h-he'd…"

"Most kids already have an All Might toy or costume. Do you know how much merch he has?"

Shouto shakes his head and gives her a watery-eyed look that makes her heart crumple.

"Well…W-well, he probably doesn't have the collectibles, and it being All Might would mean he'd treasure it more." She looks around, and perks up at a rack in the corner. "Oh! How about that!"

They approach the store's collection of All Might apparel. It's not a toy store, so they're all too big for a child, but there _is_ a _Limited run_ _Wookiees Exclusive_.

She points at the hoodie. "He definitely wouldn't have that one!"

"It's…big," Shouto frowns.

"That way he can wear it forever. I think that makes it special." She pulls it from the rack and shows him. The normally blue base is a gradient between black and blue, and the ribbed bottom is defined in gold thread. The white space at the centre of the chest looks more like a diamond than Fuyumi thinks the original costume does. It's somehow louder than the already loud design, but the dark aspect makes it look kinda cool, she thinks. When she pulls the hoodie to the front, rather than the popular two-pronged hood design, blocky yellow bars ring the edge of the hood and extend into two lines mirroring the position of the hood. There's also a "W" logo on the chest, naturally.

"It's big," Shouto repeats.

"It's rare. And subtle! He can wear it everywhere! I think a useful present will make him happy! You're the same size, right? Try it on!"

Shouto shuffles forward and takes the edge of the hoodie. She lifts it so he can slide it over his head. He shakes it a bit to get it on, and extends his arms out. The sleeves are too big for him and dangle, while the body is so big his legs seem to be vanishing into it. Still, it doesn't reach his knees.

"Perfect! Let's get it!"

"It's big," he mumbles to himself, but he still lets Fuyumi take it.

They ring it up at the counter. It's a whopping 35,000 yen, which makes Fuyumi wince even with her generous bank account. She takes out her wallet, but Shouto grasps her wrist and shakes his head firmly. She raises her eyebrows as he lifts his own wallet and reveals…

Wow. That's a lot of money.

He starts slapping 5,000 yen bills on the counter one after the other, and the clerk and Fuyumi gape with each one. Then, after reviewing the amount he gave, he nods and steps back. His wallet is still full.

The clerk lifts it, and twitches when Shouto shouts "WAIT!"

"Y…es?"

"It's a present."

The clerk looks down at the hoodie. "Oh, we don't wrap…"

Shouto's face falls.

"…We have store boxes, though!" He takes out a flat piece of cardboard, and folds it into what looks like a short shoe box. He places the hoodie in and closes it. "There. All set!"

"Thank you," Shouto nods.

"Do you…want anything for yourself?" Fuyumi asks hesitantly.

His eye goes saucer-wide. "Myself?"

"I mean, you like heroes, right?"

"Myself," he murmurs, apparently not hearing her. He runs over to the All Might wall and picks up a vest with the same size and design as the hoodie. He also selects a hairband and sweatband, and then darts back to the counter. "All these!"

Fuyumi looks at the clerk from the corner of her eye, sweat beading on the back of her neck. If they're recognized…

"Do you want this boxed…?"

"No. It's not a present." Shouto rests his chin on the counter and waits for the clothes to be checked out. Fuyumi glances at the corner consumed by Endeavor merchandise. Her father's printed face glares at her. Judging her. She slides closer to Shouto.

"Thank you for shopping at the Utility Belt!"

Fuyumi hauls ass out of there, dragging a grinning Shouto in tow. Her dad is going to _kill_ her. And then he'll find out she told Shouto to go buy himself from All Might merch himself and he'll resurrect her and kill her again!

"Hats!" She declares out loud. "Let's wear hats!"

"What about wrapping paper?" Shouto asks.

"Hats. Then we wrap."

They get hats. Fuyumi stuffs her red-licked locks into a baseball cap, and Shouto wears a newsboy cap. He fusses when Fuyumi stuffs his distinctive hair under the band, but it should be enough to keep his identity unclear, for now.

"Do you wanna wear your vest?"

Shouto nods insistently, and rips his bag open. He nearly knocks his hat off yanking his oversized spoils on. Like the hoodie, it hangs loosely off him and erases even the suggestion of a waist, but he at least looks like has shoulders. He raises his arms and presents it smugly. Definitely a rebellious streak in this kid.

"You look great!" Fuyumi cheers. "And you'll match! I bet he'll love it!"

"It's All Might," Shouto says, still smug.

"Yeah. Dad'll kill you if he sees that."

The smug look intensifies.

Well, it's official! She loves him unconditionally. If she fakes her death, she's taking Shouto, before he learns he's allowed to talk smack to her.

"Let's see, the craft shop is…" She sits up and looks around, trying to remember the layout of the mall. Clothing store, art store, clothing store, chocolate store…And wait…What's _that?_

A shadow is lingering around the last visible store, and as she tries to make it out, it grows larger. The people nearby hop out of the way as it lances across the walls, spreading up, up past its floor—

"What quirk is that?" Fuyumi wonders out loud.

"That's illegal," Shouto declares.

"Oh— yeah, you're right. Honestly, what kind of—"

The shadow hits the windowed roof, and then suddenly, the entire building goes dark.

Shouto jumps and falls into Fuyumi's arms. She squeezes him nervously and tries to make out the quirk in the remaining light coming from the mall stores. It doesn't seem to be moving anymore. Was making it dark in here just the goal?

"I think it might be a robbery," Fuyumi mumbles. "Come on, Shouto, let's go. Security should be able to handle it until a hero gets here."

She tries to push Shouto towards the door, but they both stop dead when the lights flicker. Frightened voices ring out around the mall amidst the low hum of people talking. She yanks Shouto and starts running, but stumbles into the wall when the lights all go out at once. She hits the ground and protects Shouto with her body on instinct. It's pitch black, she can't _see_ —

"The doors," Shouto whispers.

"I can't see anything," Fuyumi hisses back.

"It's a wall—" There's screaming that makes both of them jump, but it breaks down into crying. Someone having a meltdown. Fuyumi's breath stutters. She's in _middle school,_ how could she fight off a villain if one attacked her? Her quirk can't help her out of here. Her dad is going to find out she let Shouto get hospitalized or worse and then _kill her_.

Shouto squirms out from underneath her. "It's okay."

"Shouto, stay close to me, if I can't feel you I won't be able to—"

"It's okay. Because…Because _I'm_ here."

Then, with a lick of vivid orange light, Shouto's left side erupts into flames.

It's more intense than she thought. It's less bombastic than his older brother's fire, but he's holding it consistently, pure and vivid and gently licking up his side, illuminating their corner of the mall. He sticks out a finger, and a thin web of ice forms around it. Then a thick layer of ice starts to spread over it. He plucks it from his hand, sticks in a flaming finger, and a bloom of light fills the orb. He fills the hole with a cap and extinguishes the fire licking up his skin.

"When did you learn how to…?"

"It's easy. Just heroic thinking." He kneels over and rolls it along the floor, towards the door.

And then, more light.

A tentative glow at first, but then a whole spray of green orbs. Then a strike of electricity that illuminates the crowds coming from the body of an older man. Someone who's entire body is glowing emerges from one of the stores. Fuyumi breathes out a laugh as more and more people with quirks that give off light start making their way across the mall, towards the doors.

Fuyumi breathes a laugh. "Will you look at that."

The doors aren't locked, though the shadow is coating the glass. Someone holds them open and starts escorting people out. Shouto asks for a water bottle, and creates ten more orbs. He gives them to someone staying behind, to use as markers for whoever is going to find the shadow quirk user.

"A little All Might, aren't you?" The man laughs. "You're going to be a great hero."

Shouto's smile is so bright it could light up the whole mall by itself.

They sit at an outdoor table for one of the restaurants, watching the shadows creep over the glass, away from the swarm of people escaping from the front doors. She shoes away a bee and sighs. If she leaves now, chances are she'll be stuffed in a train with all these people, but they'll definitely have to close the place down to investigate. Fuyumi doesn't think she's ever seen a quirk this vast before.

Coming to a decision, she stands. "Come on, Shouto, Tokyo's a big city! I'm sure there's a street-level craft shop _somewhere_."

It's her first time spending time with this kid, and there's no _way_ she's going to squander it.

* * *

 **AN:** A Shouto chapter! Birthday will be next chapter, of course. And then... _plot_


End file.
